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Document And Entity Information - shares	9 Months Ended
Document And Entity Information - shares	Sep. 30, 2013	Oct. 22, 2013
Document Information [Line Items]
Entity Registrant Name	SEI INVESTMENTS CO
Entity Central Index Key	0000350894
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2013
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q3
Trading Symbol	SEIC
Amendment Flag	false
Entity Common Stock, Shares Outstanding		170,608,053

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2013	Dec. 31, 2012
Current Assets:
Cash and cash equivalents	$ 527,214	$ 452,247
Restricted cash	5,500	6,000
Receivables from regulated investment companies	39,579	31,084
Receivables, net of allowance for doubtful accounts of $625 and $805 (Note 4)	186,382	171,734
Deferred income taxes	1,284	2,012
Securities owned (Note 6)	20,728	20,088
Other current assets	19,345	18,239
Total Current Assets	800,032	701,404
Property and Equipment, net of accumulated depreciation of $214,653 and $201,418 (Note 4)	118,494	127,581
Capitalized Software, net of accumulated amortization of $171,015 and $149,747	313,206	307,490
Investments Available for Sale (Note 6)	86,186	75,869
Trading Securities (Note 6)	4,841	5,909
Investment in Unconsolidated Affiliates (Note 2)	57,429	77,398
Other Assets, net	11,511	14,173
Total Assets	1,391,699	1,309,824
Current Liabilities:
Accounts payable	7,275	11,248
Accrued liabilities (Note 4)	136,639	138,305
Deferred revenue	1,364	2,452
Total Current Liabilities	145,278	152,005
Deferred Income Taxes	71,151	93,458
Other Long-term Liabilities (Note 11)	8,703	7,032
Total Liabilities	225,132	252,495
Commitments and Contingencies (Note 12)
SEI Investments shareholders' equity:
Common stock, $.01 par value, 750,000 shares authorized;170,500 and 172,220 shares issued and outstanding	1,705	1,722
Capital in excess of par value	700,673	624,305
Retained earnings	462,633	405,914
Accumulated other comprehensive income, net	1,556	6,239
Total SEI Investments shareholders' equity	1,166,567	1,038,180
Noncontrolling interest	0	19,149
Total Equity	1,166,567	1,057,329
Total Liabilities and Equity	$ 1,391,699	$ 1,309,824

Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Sep. 30, 2013	Dec. 31, 2012
Current Assets:
Receivables, allowance for doubtful accounts	$ 625	$ 805
Property and Equipment, accumulated depreciation	214,653	201,418
Capitalized Software, accumulated amortization	$ 171,015	$ 149,747
SEI Investments shareholders' equity:
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	750,000	750,000
Common stock, shares issued	170,500	172,220
Common stock, shares outstanding	170,500	172,220

Consolidated Statements Of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues:
Asset management, administration and distribution fees	$ 208,780	$ 183,083	$ 611,135	$ 532,650
Information processing and software servicing fees	64,606	60,901	191,606	174,355
Transaction-based and trade execution fees	7,269	7,768	24,367	23,882
Total revenues	280,655	251,752	827,108	730,887
Expenses:
Subadvisory, distribution and other asset management costs	31,209	26,022	88,795	79,442
Software royalties and other information processing costs	7,541	6,701	22,912	19,337
Brokerage commissions	5,519	5,542	18,291	17,483
Compensation, benefits and other personnel	89,311	85,781	264,636	244,855
Stock-based compensation	11,097	3,879	26,997	11,777
Consulting, outsourcing and professional fees	33,367	27,314	98,667	80,598
Data processing and computer related	12,654	11,749	37,028	34,873
Facilities, supplies and other costs	13,573	15,129	47,280	44,909
Amortization	8,829	10,384	25,498	25,413
Depreciation	5,616	5,761	17,050	16,823
Total expenses	218,716	198,262	647,154	575,510
Income from operations	61,939	53,490	179,954	155,377
Net gain from investments	535	3,708	638	7,577
Interest and dividend income	679	1,490	2,420	4,417
Interest expense	(195)	(115)	(422)	(389)
Equity in earnings of unconsolidated affiliates	31,028	24,928	86,204	74,970
Gain on sale of subsidiary (Note 13)	0	0	22,112	0
Other income (Note 14)	0	0	43,429	0
Net income before income taxes	93,986	83,501	334,335	241,952
Income taxes	26,791	32,415	111,376	90,892
Net income	67,195	51,086	222,959	151,060
Less: Net income attributable to the noncontrolling interest	0	(343)	(350)	(797)
Net income attributable to SEI Investments Company	$ 67,195	$ 50,743	$ 222,609	$ 150,263
Basic earnings per common share	$ 0.39	$ 0.29	$ 1.29	$ 0.86
Shares used to compute basic earnings per share	171,308	173,429	172,043	174,869
Diluted earnings per common share	$ 0.38	$ 0.29	$ 1.26	$ 0.85
Shares used to compute diluted earnings per share	176,043	175,369	176,036	176,317
Dividends declared per common share	$ 0.00	$ 0.00	$ 0.20	$ 0.15

Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement of Comprehensive Income [Abstract]
Net income	$ 67,195	$ 51,086	$ 222,959	$ 151,060
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	3,146	3,464	(3,961)	4,011
Unrealized holding loss on investments:
Unrealized holding gains (losses) during the period, net of income taxes	354	586	(886)	642
Other comprehensive income (loss), reclassification adjustment for sale of securities included in net income, net of tax	55	10	(287)	(27)
Unrealized holding gain (loss) on investments:	409	596	(1,173)	615
Total other comprehensive income (loss), net of tax	3,555	4,060	(5,134)	4,626
Comprehensive income	70,750	55,146	217,825	155,686
Comprehensive (income) loss attributable to the noncontrolling interest	0	(847)	101	(1,630)
Comprehensive income attributable to SEI Investments Company	$ 70,750	$ 54,299	$ 217,926	$ 154,056

Consolidated Statements Of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement of Comprehensive Income [Abstract]
Unrealized holding gains (losses) during the period, income tax expense (benefit)	$ 111	$ 230	$ (701)	$ 307
Reclassification adjustment for losses (gains) realized in net income, income tax benefit (expense)	$ 23	$ 4	$ (162)	$ (19)

Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:
Net income	$ 222,959	$ 151,060
Adjustments to reconcile net income to net cash provided by operating activities (See Note 1)	17,336	(5,161)
Net cash provided by operating activities	240,295	145,899
Cash flows from investing activities:
Additions to property and equipment	(10,413)	(21,651)
Additions to capitalized software	(31,044)	(25,894)
Purchases of marketable securities	(48,653)	(22,505)
Prepayments and maturities of marketable securities	29,462	36,938
Sales of marketable securities	7,284	910
Purchases of other investments	(2,604)	(2,568)
Sale of subsidiary, net of cash transferred (See Note 13)	6,028	0
Net cash used in investing activities	(49,940)	(34,770)
Cash flows from financing activities:
Purchase and retirement of common stock	(144,121)	(111,593)
Proceeds from issuance of common stock	54,788	30,624
Tax benefit on stock options exercised	8,345	(834)
Payment of dividends	(34,400)	(52,635)
Net cash used in financing activities	(115,388)	(134,438)
Net increase (decrease) in cash and cash equivalents	74,967	(23,309)
Cash and cash equivalents, beginning of period	452,247	420,986
Cash and cash equivalents, end of period	$ 527,214	$ 397,677

Summary Of Significant Accounting Policies

9 Months Ended

Sep. 30, 2013

Accounting Policies [Abstract]

Summary Of Significant Accounting Policies

Summary of Significant Accounting Policies

Nature of Operations

SEI Investments Company (the Company), a Pennsylvania corporation, provides investment processing, investment management, and investment operations solutions to corporations, financial institutions, financial advisors, and ultra-high-net-worth families in the United States, Canada, the United Kingdom, continental Europe, and other various locations throughout the world. Investment processing solutions consist of application and business process outsourcing services, professional services and transaction-based services. Revenues from investment processing solutions are recognized in Information processing and software servicing fees on the accompanying Consolidated Statements of Operations, except for fees earned associated with trade execution services.

Investment management programs consist of mutual funds, alternative investments and separate accounts. These include a series of money market, equity, fixed-income and alternative investment portfolios, primarily in the form of registered investment companies. The Company serves as the administrator and investment advisor for many of these products. Revenues from investment management programs are recognized in Asset management, administration and distribution fees on the accompanying Consolidated Statements of Operations.

Investment operations solutions offer investment managers support for traditional investment products such as mutual funds, collective investment trusts, exchange-traded funds, and institutional and separate accounts, by providing outsourcing services including fund and investment accounting, administration, reconciliation, investor servicing and client reporting. These solutions also provide support to managers focused on alternative investments who manage hedge funds, funds of hedge funds, private equity funds and real estate funds, across registered, partnership and separate account structures domiciled in the United States and overseas. Revenues from investment operations solutions are recognized in Asset management, administration and distribution fees on the accompanying Consolidated Statements of Operations.

On July 31, 2012, the Company entered into a definitive agreement to sell all ownership interest in the asset management firm SEI Asset Korea (SEI AK), a joint venture located in South Korea. The Company's ownership interest in SEI AK was 56.1 percent. On March 28, 2013, all conditions subject to closing the transaction were satisfied and all ownership interests in SEI AK were transferred to the buyer (See Note 13).

Basis of Presentation

The accompanying Consolidated Financial Statements have been prepared in accordance with accounting principles generally accepted in the United States of America. Certain financial information and accompanying note disclosure normally included in the Company’s Annual Report on Form 10-K has been condensed or omitted. The interim financial information is unaudited but reflects all adjustments (consisting of only normal recurring adjustments) which are, in the opinion of management, necessary for a fair statement of financial position of the Company as of September 30, 2013, the results of operations for the three and nine months ended September 30, 2013 and 2012, and cash flows for the nine month periods ended September 30, 2013 and 2012. These interim Consolidated Financial Statements should be read in conjunction with the audited Consolidated Financial Statements and the Notes to the Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2012.

There have been no significant changes in significant accounting policies during the nine months ended September 30, 2013 as compared to the significant accounting policies described in the Company’s Annual Report on Form 10-K for the year ended December 31, 2012.

Cash and Cash Equivalents

Cash and cash equivalents includes $368,819 and $247,314 at September 30, 2013 and December 31, 2012, respectively, primarily invested in SEI-sponsored open-ended money market mutual funds. The SEI-sponsored mutual funds are considered Level 1 assets.

Restricted Cash

Restricted cash includes $5,000 at September 30, 2013 and December 31, 2012 segregated for regulatory purposes related to trade-execution services conducted by SEI Investments (Europe) Limited. Restricted cash also includes $500 and $1,000 at September 30, 2013 and December 31, 2012, respectively, segregated in special reserve accounts for the benefit of customers of the Company’s broker-dealer subsidiary, SEI Investments Distribution Co. (SIDCO), in accordance with certain rules established by the Securities and Exchange Commission for broker-dealers.

Capitalized Software

The Company capitalized $31,044 and $25,894 of software development costs during the nine months ended September 30, 2013 and 2012, respectively. As of September 30, 2013, capitalized software placed into service included on the accompanying Consolidated Balance Sheet had a weighted average remaining life of approximately 8.8 years. Amortization expense related to capitalized software was $25,328 and $24,858 during the nine months ended September 30, 2013 and 2012, respectively.

Software development costs capitalized during the nine months ended September 30, 2013 and 2012 relates to the continued development of the SEI Wealth Platform^SM(the Platform), formerly known as the Global Wealth Platform or GWP. As of September 30, 2013, the net book value of the Platform was $307,121, net of accumulated amortization of $140,925. Capitalized software development costs in-progress at September 30, 2013 associated with future releases to the Platform were $5,943. The Platform has an estimated useful life of 15 years and a weighted average remaining life of 8.8 years. Amortization expense for the Platform was $25,046 and $24,506 during the nine months ended September 30, 2013 and 2012, respectively. During the three months ended September 30, 2012, the Company decided to discontinue the use of specific functionality within the Platform by the end of the September 2012 and expensed the remaining net book value of $2,661 related to previously capitalized software development costs of the component. This cost is included in total amortization expense during the nine months ended September 30, 2012.

Earnings per Share

The calculations of basic and diluted earnings per share for the three months ended September 30, 2013 and 2012 are:



	For the Three Months Ended September 30, 2013
	Income (Numerator)		Shares (Denominator)	Per Share Amount
Basic earnings per common share	$	67,195	171,308	$	0.39
Dilutive effect of stock options	—		4,735
Diluted earnings per common share	$	67,195	176,043	$	0.38



	For the Three Months Ended September 30, 2012
	Income (Numerator)		Shares (Denominator)	Per Share Amount
Basic earnings per common share	$	50,743	173,429	$	0.29
Dilutive effect of stock options	—		1,940
Diluted earnings per common share	$	50,743	175,369	$	0.29

Employee stock options to purchase 3,042,000 and 9,552,000 shares of common stock, with an average exercise price of $31.39 and $26.51, were outstanding during the three months ended September 30, 2013 and 2012, respectively, but not included in the computation of diluted earnings per common share because the effect on diluted earnings per common share would have been anti-dilutive.



	For the Nine Months Ended September 30, 2013
	Income (Numerator)		Shares (Denominator)	Per Share Amount
Basic earnings per common share	$	222,609	172,043	$	1.29
Dilutive effect of stock options	—		3,993
Diluted earnings per common share	$	222,609	176,036	$	1.26



	For the Nine Months Ended September 30, 2012
	Income (Numerator)		Shares (Denominator)	Per Share Amount
Basic earnings per common share	$	150,263	174,869	$	0.86
Dilutive effect of stock options	—		1,448
Diluted earnings per common share	$	150,263	176,317	$	0.85

Employee stock options to purchase 5,522,000 and 13,908,000 shares of common stock, with an average exercise price of $29.22 and $23.40, were outstanding during the nine months ended September 30, 2013 and 2012, respectively, but not included in the computation of diluted earnings per common share because the effect on diluted earnings per common share would have been anti-dilutive.

Statements of Cash Flows

For purposes of the Consolidated Statements of Cash Flows, the Company considers investment instruments purchased with an original maturity of three months or less to be cash equivalents.

The following table provides the details of the adjustments to reconcile net income to net cash provided by operating activities for the nine months ended September 30:



	2013			2012
Net income	$	222,959		$	151,060
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	17,050			16,823
Amortization	25,498			25,413
Equity in earnings of unconsolidated affiliates	(86,204		)	(74,970		)
Distributions received from unconsolidated affiliate	109,173			72,306
Stock-based compensation	26,997			11,777
Provision for losses on receivables	(180		)	(112		)
Deferred income tax expense	(21,443		)	2,117
Gain from sale of SEI AK (See Note 13)	(22,112		)	—
Net gain from investments	(638		)	(7,577		)
Change in other long-term liabilities	1,671			2,803
Change in other assets	80			(1,063		)
Other	(4,199		)	4,759
Change in current asset and liabilities
Decrease (increase) in
Restricted cash for broker-dealer operations	500			—
Receivables from regulated investment companies	(8,495		)	(3,203		)
Receivables	(17,255		)	(54,995		)
Other current assets	(1,208		)	(863		)
Increase (decrease) in
Accounts payable	(3,960		)	1,568
Accrued liabilities	3,149			967
Deferred revenue	(1,088		)	(911		)
Total adjustments	17,336			(5,161		)
Net cash provided by operating activities	$	240,295		$	145,899

Reclassifications

Certain prior year amounts have been reclassified to conform to current year presentation.

Investment In Unconsolidated Affiliates

9 Months Ended

Sep. 30, 2013

Equity Method Investments and Joint Ventures [Abstract]

Investment In Unconsolidated Affiliates

Investment in Unconsolidated Affiliates

LSV Asset Management

The Company has an investment in the general partnership LSV Asset Management (LSV). LSV is a registered investment advisor that provides investment advisory services to institutions, including pension plans and investment companies. LSV is currently an investment sub-advisor for a small number of SEI-sponsored mutual funds. The Company accounts for its interest in LSV using the equity method because of its less than 50 percent ownership. The Company’s interest in the net assets of LSV is reflected in Investment in unconsolidated affiliates on the accompanying Consolidated Balance Sheets and its interest in the earnings of LSV is reflected in Equity in earnings of unconsolidated affiliates on the accompanying Consolidated Statements of Operations.

As of December 31, 2012, the Company’s total partnership interest in LSV was approximately 39.8 percent. In March 2009, certain partners (the Contributing partners) of LSV, including the Company, designated a portion of their partnership interest for the purpose of providing an interest in the partnership to a select group of key employees. Until such time an interest in the partnership is issued to a key employee, all profits, losses, distributions and other rights and obligations relating to such unissued interests remains with the Contributing partners. Each issuance must be authorized by unanimous vote of all Contributing partners. In April 2013, the Contributing partners agreed to provide certain key employees an interest in LSV, thereby reducing the Company’s interest in LSV to approximately 39.3 percent. This issuance reflected the remaining amount of the designated partnership interest of the Contributing partners.

At September 30, 2013, the Company’s total investment in LSV was $46,414. The investment in LSV exceeded the underlying equity in the net assets of LSV by $3,062 which is considered goodwill embedded in the investment. The Company receives partnership distributions from LSV on a quarterly basis. The Company received partnership distribution payments from LSV for $109,173 and $72,306 in the nine months ended September 30, 2013 and 2012, respectively. The Company received an additional partnership distribution payment from LSV during the nine months ended September 30, 2013 as compared to the prior year period due to a change in the timing of the payments.

The Company’s proportionate share in the earnings of LSV was $31,285 and $24,928 during the three months ended September 30, 2013 and 2012, respectively. During the nine months ended September 30, 2013 and 2012, the Company’s proportionate share in the earnings of LSV was $86,871 and $74,970, respectively.

The following table contains the condensed statements of operations of LSV for the three and nine months ended September 30, 2013 and 2012:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2013		2012		2013		2012
Revenues	$	92,184	$	74,163	$	256,782	$	220,817
Net income	79,555		62,946		220,657		186,991

Guaranty Agreement with LSV Employee Group II

In April 2011, LSV Employee Group II agreed to purchase a partnership interest of an existing LSV employee for $4,300, of which $3,655 was financed through a term loan with Bank of America, N.A. (Bank of America). The Company provided an unsecured guaranty to the lenders of all the obligations of LSV Employee Group II. The lenders have the right to seek payment from the Company in the event of a default by LSV Employee Group II.

As of October 22, 2013, the remaining unpaid principal balance of the term loan was $1,026. LSV Employee Group II has met all financial obligations to date regarding the scheduled repayment of the term loan since its origination. The Company, in its capacity as guarantor, currently has no obligation of payment relating to the term loan of LSV Employee Group II and, furthermore, fully expects that LSV Employee Group II will meet all of their future obligations regarding the term loan.

Guaranty Agreement with LSV Employee Group III

In October 2012, LSV Employee Group III purchased a portion of the partnership interest of three existing LSV employees for $77,700, of which $69,930 was financed through two syndicated term loan facilities contained in a credit agreement with The PrivateBank and Trust Company. The Company provided an unsecured guaranty for $45,000 of the obligations of LSV Employee Group III to the lenders through a guaranty agreement. The lenders have the right to seek payment from the Company in the event of a default by LSV Employee Group III. LSV agreed to provide an unsecured guaranty for $24,930 of the obligations of LSV Employee Group III to the lenders through a separate guaranty agreement.

As of October 22, 2013, the remaining unpaid principal balances of the term loans guaranteed by LSV and the Company were $13,086 and $45,000, respectively. LSV Employee Group III has met all financial obligations to date regarding the scheduled repayment of the term loans since origination. The Company, in its capacity as guarantor, currently has no obligation of payment relating to the term loan of LSV Employee Group III and, furthermore, fully expects that LSV Employee Group III will meet all of their future obligations regarding the term loan.

Investment in Gao Fu Limited

The Company has an investment in Gao Fu Limited (Gao Fu), a wealth services firm based in Shanghai in the Republic of China. The Company accounts for its interest in Gao Fu using the equity method. At September 30, 2013, the Company's total investment in Gao Fu was $11,015. The Company's proportionate share in the losses of Gao Fu was $257 and $667 during the three and nine months ended September 30, 2013, respectively.

Variable Interest Entities - Investment Products	9 Months Ended
Variable Interest Entities - Investment Products	Sep. 30, 2013
Variable Interest Entities - Investment Products [Abstract]
Variable Interest Entities - Investment Products	Variable Interest Entities – Investment Products The Company has created numerous investment products for its clients in various types of legal entity structures. The Company serves as the Manager, Administrator and Distributor for these investment products and may also serve as the Trustee for some of the investment products. Clients are the equity investors and participate in proportion to their ownership percentage in the net income and net capital gains of the products, and, on liquidation, will participate in proportion to their ownership percentage in the remaining net assets of the products after satisfaction of outstanding liabilities. Some of the Company’s investment products have been determined to be VIEs at inception. The Company does not have a significant equity investment in any of the VIEs and does not have an obligation to enter into any guarantee agreements with the VIEs. The Company is not the primary beneficiary of the VIEs because the expected fees and the expected return on any investment into the VIE by the Company relative to the expected returns of the VIE to the equity investor holders does not approach 50 percent of the expected losses or gains of the VIEs. Therefore, the Company is not required to consolidate any investment products that are VIEs into its financial statements. The Company’s variable interest in the VIEs, which consists of management fees and in some situations, seed capital, is not considered a significant variable interest. The risks to the Company associated with its involvement with any of the investment products that are VIEs are limited to the cash flows received from the revenue generated for asset management, administration and distribution services and any equity investments in the VIEs. Both of these items are not significant. The Company has no other financial obligation to the VIEs. Amounts relating to fees due from the VIEs included in Receivables and amounts relating to equity investments in the VIEs included in Investments Available for Sale on the Company’s Consolidated Balance Sheets are not significant to the total assets of the Company.

Composition Of Certain Financial Statement Captions

9 Months Ended

Sep. 30, 2013

Items Included in Consolidated Statement of Financial Condition [Abstract]

Composition Of Certain Financial Statement Captions

Composition of Certain Financial Statement Captions

Receivables

Receivables on the accompanying Consolidated Balance Sheets consist of:



	September 30, 2013			December 31, 2012
Trade receivables	$	46,855		$	46,650
Fees earned, not billed	126,943			116,019
Other receivables	13,209			9,870
	187,007			172,539
Less: Allowance for doubtful accounts	(625		)	(805		)
	$	186,382		$	171,734

Fees earned, not billed represents receivables earned but unbilled and results from timing differences between services provided and contractual billing schedules. These billing schedules generally provide for fees to be billed on a quarterly basis. In addition, certain fees earned from investment operations services are calculated based on assets under administration that have a prolonged valuation process which delays billings to clients.

Receivables from regulated investment companies on the accompanying Consolidated Balance Sheets primarily represent fees receivable for distribution, investment advisory, and administration services to various regulated investment companies sponsored by SEI.

Property and Equipment

Property and Equipment on the accompanying Consolidated Balance Sheets consists of:



	September 30, 2013			December 31, 2012
Buildings	$	138,106		$	137,751
Equipment	67,182			66,167
Land	9,929			9,929
Purchased software	95,448			91,468
Furniture and fixtures	16,909			18,535
Leasehold improvements	4,467			5,037
Construction in progress	1,106			112
	333,147			328,999
Less: Accumulated depreciation	(214,653		)	(201,418		)
Property and Equipment, net	$	118,494		$	127,581

The Company recognized $17,050 and $16,823 in depreciation expense related to property and equipment for the nine months ended September 30, 2013 and 2012, respectively.

Accrued Liabilities

Accrued liabilities on the accompanying Consolidated Balance Sheets consist of:



	September 30, 2013		December 31, 2012
Accrued employee compensation	$	55,729	$	63,996
Accrued employee benefits and other personnel	8,644		7,299
Accrued consulting, outsourcing and professional fees	21,606		16,676
Accrued brokerage fees	5,045		5,733
Accrued sub-advisory, distribution and other asset management fees	23,839		17,548
Accrued income taxes	26		104
Other accrued liabilities	21,750		26,949
Total accrued liabilities	$	136,639	$	138,305

Fair Value Measurements

9 Months Ended

Sep. 30, 2013

Fair Value Disclosures [Abstract]

Fair Value Measurements

The fair value of the Company’s financial assets and liabilities is determined in accordance with the fair value hierarchy. The fair value of the Company’s Level 1 financial assets consist mainly of investments in equity and fixed-income mutual funds that are quoted daily. Level 2 financial assets consist of Government National Mortgage Association (GNMA) mortgage-backed pass-through certificates, Federal Home Loan Bank (FHLB) and other U.S. government agency short-term notes and investment grade commercial paper. The Company's Level 2 financial assets, with the exception of the GNMA securities, were purchased as part of a cash management program requiring only short term, top-tier investment grade government and corporate securities. The GNMA mortgage-backed pass-through certificates were purchased for the sole purpose of satisfying specific regulatory requirements imposed on our wholly-owned limited purpose federal thrift subsidiary, SEI Private Trust Company (SPTC). As a result, the Company's Level 2 financial assets are limited to only these types of fixed income securities. The valuation of the Company's Level 2 financial assets are based upon securities pricing policies and procedures utilized by third-party pricing vendors. The pricing policies and procedures applied during the nine months ended September 30, 2013 were consistent with those as described in our Annual Report on Form 10-K at December 31, 2012. The Company's Level 3 financial assets at December 31, 2012 consisted of an investment product that was in the process of liquidation and was closed to new investors. The Company had no Level 3 financial assets at September 30, 2013 and had no Level 3 financial liabilities at September 30, 2013 or December 31, 2012. There were no transfers of financial assets between levels within the fair value hierarchy during the nine months ended September 30, 2013.

The fair value of certain financial assets and liabilities of the Company was determined using the following inputs:



	At September 30, 2013
	Fair Value Measurements at Reporting Date Using
Assets	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Equity available-for-sale securities	$	10,644	$	10,644	$	—	$	—
Fixed income available-for-sale securities	75,542		—		75,542		—
Fixed income securities owned	20,728		—		20,728		—
Trading securities	4,841		4,841		—		—
	$	111,755	$	15,485	$	96,270	$	—



	At December 31, 2012
	Fair Value Measurements at Reporting Date Using
Assets	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Equity available-for-sale securities	$	15,926	$	15,926	$	—	$	—
Fixed income available-for-sale securities	59,943		—		59,943		—
Fixed income securities owned	20,088		—		20,088		—
Trading securities	5,909		4,706		—		1,203
	$	101,866	$	20,632	$	80,031	$	1,203

The table below presents a reconciliation for all assets and liabilities of the Company measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the period from January 1, 2013 to September 30, 2013:



	Trading Securities
Balance, January 1, 2013	$	1,203
Purchases	—
Issuances	—
Principal prepayments and settlements	(1,167		)
Sales	—
Total gains or (losses) (realized/unrealized):
Included in earnings	(36		)
Included in other comprehensive income	—
Transfers in and out of Level 3	—
Balance, September 30, 2013	$	—



	Trading Securities
Balance, January 1, 2012	$	52,623
Purchases	—
Issuances	—
Principal prepayments and settlements	(9,833		)
Sales	—
Total gains or (losses) (realized/unrealized):
Included in earnings	7,303
Included in other comprehensive income	—
Transfers in and out of Level 3	—
Balance, September 30, 2012	$	50,093

Marketable Securities

9 Months Ended

Sep. 30, 2013

Marketable Securities [Abstract]

Marketable Securities

Investments Available for Sale

Investments available for sale classified as non-current assets consist of:



	At September 30, 2013
	Cost Amount		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
SEI-sponsored mutual funds	$	7,148	$	873	$	—	$	8,021
Equities and other mutual funds	2,589		34		—		2,623
Debt securities	74,102		1,440		—		75,542
	$	83,839	$	2,347	$	—	$	86,186



	At December 31, 2012
	Cost Amount		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
SEI-sponsored mutual funds	$	12,953	$	376	$	(13	)	$	13,316
Equities and other mutual funds	2,610		—		—			2,610
Debt securities	55,923		4,020		—			59,943
	$	71,486	$	4,396	$	(13	)	$	75,869

Net unrealized holding gains at September 30, 2013 and December 31, 2012 were $1,656 (net of income tax expense of $691) and $2,829 (net of income tax expense of $1,554), respectively. These net unrealized gains are reported as a separate component of Accumulated other comprehensive income on the accompanying Consolidated Balance Sheets.

There were gross realized gains of $710 and gross realized losses of $261 from available-for-sale securities during the nine months ended September 30, 2013. There were no material gross realized gains or losses from available-for-sale securities during the nine months ended September 30, 2012. Gains and losses from available-for-sale securities, including amounts reclassified from accumulated comprehensive income, are reflected in Net gain from investments on the accompanying Consolidated Statements of Operations.

The Company’s debt securities classified as available-for-sale securities are issued by GNMA and are backed by the full faith and credit of the U.S. government. These securities were purchased to satisfy applicable regulatory requirements of SPTC and have maturity dates which range from 2020 to 2043.

Trading Securities

The Company records all of its trading securities on the accompanying Consolidated Balance Sheets at fair value. Unrealized gains and losses from the change in fair value of these securities are recognized in Net gain from investments on the accompanying Consolidated Statements of Operations.

Trading securities of the Company primarily consist of an investment related to the startup of mutual funds sponsored by LSV. These mutual funds are U.S. dollar denominated funds that invests primarily in securities of Canadian and Australian companies as well as various other global securities. The underlying securities held by the funds are translated into U.S. dollars within the funds. The funds had a fair value of $4,841 and $4,706 at September 30, 2013 and December 31, 2012, respectively. The Company recognized gains of $135 and $520 from the change in fair value of the funds during the nine months ended September 30, 2013 and 2012, respectively. During the three months ended September 30, 2013 and 2012, the Company recognized gains of $610 and $357, respectively, from the change in fair value of the funds.

During the nine months ended September 30, 2012, the Company recognized gains from structured investment vehicle (SIV) securities of $7,343. The gains from SIV securities are reflected in Net gain from investments on the accompanying Consolidated Statements of Operations. In November 2012, the Company sold its remaining SIV securities and no longer owns any SIV securities.

Securities Owned

The Company’s broker-dealer subsidiary, SIDCO, has investments in U.S. government agency and commercial paper securities with maturity dates less than one year. These investments are reflected as Securities owned on the accompanying Consolidated Balance Sheets. Due to specialized accounting practices applicable to investments by broker-dealers, the securities are reported at fair value and changes in fair value are recorded in current period earnings. The securities had a fair value of $20,728 and $20,088 at September 30, 2013 and December 31, 2012, respectively. There were no material net gains or losses from the change in fair value of the securities during the three and nine months ended September 30, 2013 and 2012.

Lines Of Credit	9 Months Ended
Lines Of Credit	Sep. 30, 2013
Line of Credit Facility [Abstract]
Lines Of Credit	Lines of Credit The Company has a five-year $300,000 Credit Agreement (the Credit Facility) with Wells Fargo Bank, National Association, and a syndicate of other lenders. The Credit Facility is scheduled to expire in February 2017, at which time any aggregate principal amount of loans outstanding becomes payable in full. Any borrowings made under the Credit Facility will accrue interest at 1.25 percent above LIBOR. There is also a commitment fee equal to 0.15 percent per annum on the daily unused portion of the facility. The aggregate amount of the Credit Facility may be increased by an additional $100,000 under certain conditions set forth in the agreement. The Credit Facility contains covenants that restrict the ability of the Company to engage in mergers, consolidations, asset sales, investments, transactions with affiliates, or to incur liens, as defined in the agreement. In the event of a default under the Credit Facility, the Company would also be restricted from paying dividends on, or repurchasing, its common stock without the approval of the lenders. None of the covenants of the Credit Facility negatively affect the Company’s liquidity or capital resources. Both the interest rate and commitment fee prices may increase if the Company’s leverage ratio reaches certain levels. Upon the occurrence of certain financial or economic events, significant corporate events, or certain other events of default constituting an event of default under the Credit Facility, all loans outstanding may be declared immediately due and payable and all commitments under the agreement may be terminated. The Company had no borrowings through the Credit Facility at September 30, 2013. The Company was in compliance with all covenants of the Credit Facility at September 30, 2013. The Company’s Canadian subsidiary has a credit facility agreement (the Canadian Credit Facility) for the purpose of facilitating the settlement of mutual fund transactions. The Canadian Credit Facility has no stated expiration date. The amount of the facility is limited to $2,000 Canadian dollars or the equivalent amount in U.S. dollars. The Canadian Credit Facility does not contain any covenants which restrict the liquidity or capital resources of the Company. The Company had no borrowings under the Canadian Credit Facility at September 30, 2013. The Company was in compliance with all covenants of the Canadian Credit Facility at September 30, 2013.

Shareholders' Equity

9 Months Ended

Sep. 30, 2013

Stockholders' Equity Note [Abstract]

Shareholders' Equity

Shareholders’ Equity

Stock-Based Compensation

The Company currently has one active equity compensation plan, the 2007 Equity Compensation Plan (the 2007 Plan), which provides for the grant of incentive stock options, non-qualified stock options and stock appreciation rights with respect to up to 20 million shares of common stock of the Company, subject to adjustment for stock splits, reclassifications, mergers and other events. Permitted grantees under the 2007 Plan include employees, non-employee directors and consultants who perform services for the Company. The plan is administered by the Compensation Committee of the Board of Directors of the Company. The Company has only granted non-qualified stock options under the plan. All outstanding stock options have performance-based vesting provisions specific to each option grant that tie the vesting of the applicable stock options to the Company’s financial performance. The Company’s stock options vest at a rate of 50 percent when specified diluted earnings per share targets are achieved, and the remaining 50 percent when secondary, higher specified diluted earnings per share targets are achieved. The amount of stock-based compensation expense is based upon management’s estimate of when the earnings per share targets may be achieved.

The Company discontinued any further grants under the Company’s 1998 Equity Compensation Plan (the 1998 Plan) as a result of the approval of the 2007 Plan. No options are available for grant from this plan. Grants made from the 1998 Plan continue in effect under the terms of the grant.

The Company recognized stock-based compensation expense in its Consolidated Financial Statements in the three and nine months ended September 30, 2013 and 2012, respectively, as follows:



	Three Months Ended September 30,						Nine Months Ended September 30,
	2013			2012			2013			2012
Stock-based compensation expense	$	11,097		$	3,879		$	26,997		$	11,777
Less: Deferred tax benefit	(4,125		)	(1,573		)	(9,908		)	(4,381		)
Stock-based compensation expense, net of tax	$	6,972		$	2,306		$	17,089		$	7,396

As of September 30, 2013, there was approximately $29,229 of unrecognized compensation cost remaining, adjusted for estimated forfeitures, related to unvested employee stock options that management expects will vest and is being amortized.

During the nine months ended September 30, 2013, the Company revised its previous estimate made as of December 31, 2012 of when certain vesting targets are expected to be achieved. This change in management's estimate resulted in an increase of $13,440 in stock-based compensation expense in the nine months ended September 30, 2013.

The Company issues new common shares associated with the exercise of stock options. The total intrinsic value of options exercised during the nine months ended September 30, 2013 was $37,171. The total options exercisable as of September 30, 2013 had an intrinsic value of $82,557. The total intrinsic value for options exercisable is calculated as the difference between the market value of the Company’s common stock as of September 30, 2013 and the weighted average exercise price of the shares. The market value of the Company’s common stock as of September 30, 2013 was $30.91 as reported by the Nasdaq Stock Market, LLC. The weighted average exercise price of the options exercisable as of September 30, 2013 was $18.54. Total options that were outstanding and exercisable as of September 30, 2013 were 22,146,000 and 6,676,000, respectively.

Common Stock Buyback

The Company’s Board of Directors, under multiple authorizations, has authorized the repurchase of the Company’s common stock on the open market or through private transactions. The Company purchased 4,879,000 shares at a total cost of $145,269 during the nine months ended September 30, 2013. As of September 30, 2013, the Company has $45,744 of authorization remaining for the purchase of common stock under the program.

The Company immediately retires its common stock when purchased. Upon retirement, the Company reduces Capital in excess of par value for the average capital per share outstanding and the remainder is charged against Retained earnings. If the Company reduces its Retained earnings to zero, any subsequent purchases of common stock will be charged entirely to Capital in excess of par value.

Cash Dividend

On May 22, 2013, the Board of Directors declared a cash dividend of $0.20 per share on the Company's common stock, which was paid on June 25, 2013, to shareholders of record on June 17, 2013. Cash dividends declared during the nine months ended September 30, 2013 and 2012 were $34,400 and $26,117, respectively.

Noncontrolling Interest

The following table provides a reconciliation of Noncontrolling interest on the Consolidated Balance Sheet for the period from January 1, 2013 to September 30, 2013:



	Noncontrolling interest
Balance, January 1, 2013	$	19,149
Net income attributable to noncontrolling interest	350
Foreign currency translation adjustments	(451		)
Sale of subsidiary (See Note 13)	(19,048		)
Balance, September 30, 2013	$	—

The following table provides a reconciliation of Noncontrolling interest on the Consolidated Balance Sheet for the period from January 1, 2012 to September 30, 2012:



	Noncontrolling interest
Balance, January 1, 2012	$	16,143
Net income attributable to noncontrolling interest	797
Foreign currency translation adjustments	833
Balance, September 30, 2012	$	17,773

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

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+ Details

Accumulated Comprehensive Income (Loss)

9 Months Ended

Sep. 30, 2013

Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]

Accumulated Comprehensive Income (Loss)

Accumulated Comprehensive Income

Accumulated other comprehensive income, net of tax, consists of:



	Foreign Currency Translation Adjustments			Unrealized Holding Gains (Losses) on Investments			Accumulated Other Comprehensive (Loss) Income
Total accumulated comprehensive income at December 31, 2012	$	3,861		$	2,829		$	6,690
Less: Total accumulated comprehensive income attributable to noncontrolling interest at December 31, 2012	(451		)	—			(451		)
Total accumulated comprehensive income attributable to SEI Investments Company at December 31, 2012	$	3,410		$	2,829		$	6,239

Total comprehensive loss for the nine months ended September 30, 2013	$	(3,961	)	$	(1,173	)	$	(5,134	)
Less: Total comprehensive loss attributable to noncontrolling interest for the nine months ended September 30, 2013	451			—			451
Total comprehensive loss attributable to SEI Investments Company for the nine months ended September 30, 2013	$	(3,510	)	$	(1,173	)	$	(4,683	)

Total accumulated comprehensive income at September 30, 2013	$	(100	)	$	1,656		$	1,556
Less: Total accumulated comprehensive income attributable to noncontrolling interest at September 30, 2013	—			—			—
Total accumulated comprehensive income attributable to SEI Investments Company at September 30, 2013	$	(100	)	$	1,656		$	1,556

- Definition

The entire disclosure for comprehensive income, which includes, but is not limited to, 1) the amount of income tax expense or benefit allocated to each component of other comprehensive income, including reclassification adjustments, 2) the reclassification adjustments for each classification of other comprehensive income and 3) the ending accumulated balances for each component of comprehensive income.

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+ Details

Business Segment Information

9 Months Ended

Sep. 30, 2013

Segment Reporting [Abstract]

Business Segment Information

The Company’s reportable business segments are:

Private Banks – provides investment processing and investment management programs to banks and trust institutions worldwide, independent wealth advisers located in the United Kingdom, and financial advisors in Canada;

Investment Advisors – provides investment management programs to affluent investors through a network of independent registered investment advisors, financial planners, and other investment professionals in the United States;

Institutional Investors – provides investment management programs and administrative outsourcing solutions to retirement plan sponsors, hospitals, and not-for-profit organizations worldwide;

Investment Managers – provides investment operations outsourcing solutions to investment managers, fund companies and banking institutions located in the United States, and to investment managers worldwide of alternative asset classes such as hedge funds, funds of hedge funds, and private equity funds across both registered and partnership structures; and

Investments in New Businesses – provides investment management programs to ultra-high-net-worth families residing in the United States through the SEI Wealth Network^® and conducts other research and development activities.

The information in the following tables is derived from the Company’s internal financial reporting used for corporate management purposes. There are no inter-segment revenues for the three and nine months ended September 30, 2013 and 2012. Management evaluates Company assets on a consolidated basis during interim periods. The accounting policies of the reportable business segments are the same as those described in Note 1 to the Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2012.

The following tables highlight certain unaudited financial information about each of the Company’s business segments for the three months ended September 30, 2013 and 2012.



	Private Banks		Investment Advisors		Institutional Investors		Investment Managers		Investments In New Businesses			Total
	For the Three Months Ended September 30, 2013
Revenues	$	97,370	$	61,393	$	63,539	$	57,266	$	1,087		$	280,655
Expenses	95,579		33,768		33,058		37,763		4,146			204,314
Operating profit (loss)	$	1,791	$	27,625	$	30,481	$	19,503	$	(3,059	)	$	76,341



	Private Banks		Investment Advisors		Institutional Investors		Investment Managers		Investments In New Businesses			Total
	For the Three Months Ended September 30, 2012
Revenues	$	92,076	$	51,384	$	58,081	$	49,311	$	900		$	251,752
Expenses	91,209		30,114		29,654		32,122		3,698			186,797
Operating profit (loss)	$	867	$	21,270	$	28,427	$	17,189	$	(2,798	)	$	64,955

A reconciliation of the total operating profit reported for the business segments to income from operations in the Consolidated Statements of Operations for the three months ended September 30, 2013 and 2012 is as follows:



	2013			2012
Total operating profit from segments above	$	76,341		$	64,955
Corporate overhead expenses	(14,402		)	(11,668		)
Noncontrolling interest reflected in segments	—			203
Income from operations	$	61,939		$	53,490

The following tables provide additional information for the three months ended September 30, 2013 and 2012 pertaining to our business segments:



	Capital Expenditures				Depreciation
	2013		2012		2013		2012
Private Banks	$	9,376	$	8,248	$	3,799	$	3,911
Investment Advisors	3,513		2,797		521		503
Institutional Investors	777		647		222		252
Investment Managers	1,596		927		525		500
Investments in New Businesses	186		140		442		449
Total from business segments	$	15,448	$	12,759	$	5,509	$	5,615
Corporate overhead	259		228		107		146
	$	15,707	$	12,987	$	5,616	$	5,761



	Amortization
	2013		2012
Private Banks	$	5,704	$	7,660
Investment Advisors	2,105		1,832
Institutional Investors	326		302
Investment Managers	218		201
Investments in New Businesses	419		332
Total from business segments	$	8,772	$	10,327
Corporate overhead	57		57
	$	8,829	$	10,384

The following tables highlight certain unaudited financial information about each of the Company’s business segments for the nine months ended September 30, 2013 and 2012.



	Private Banks		Investment Advisors		Institutional Investors		Investment Managers		Investments In New Businesses			Total
	For the Nine Months Ended September 30, 2013
Revenues	$	291,258	$	175,868	$	190,385	$	166,542	$	3,055		$	827,108
Expenses	289,632		98,291		97,595		109,432		11,774			606,724
Operating profit (loss)	$	1,626	$	77,577	$	92,790	$	57,110	$	(8,719	)	$	220,384
Gain on sale of subsidiary	22,112		—		—		—		—			22,112
Total profit (loss)	$	23,738	$	77,577	$	92,790	$	57,110	$	(8,719	)	$	242,496



	Private Banks		Investment Advisors		Institutional Investors		Investment Managers		Investments In New Businesses			Total
	For the Nine Months Ended September 30, 2012
Revenues	$	268,367	$	150,227	$	167,293	$	142,235	$	2,765		$	730,887
Expenses	263,612		88,440		86,494		92,711		11,080			542,337
Operating profit (loss)	$	4,755	$	61,787	$	80,799	$	49,524	$	(8,315	)	$	188,550

A reconciliation of the total operating profit reported for the business segments to income from operations in the Consolidated Statements of Operations for the nine months ended September 30, 2013 and 2012 is as follows:



	2013			2012
Total operating profit from segments above	$	220,384		$	188,550
Corporate overhead expenses	(40,719		)	(33,830		)
Noncontrolling interest reflected in segments	289			657
Income from operations	$	179,954		$	155,377

The following tables provide additional information for the nine months ended September 30, 2013 and 2012 pertaining to our business segments:



	Capital Expenditures				Depreciation
	2013		2012		2013		2012
Private Banks	$	26,079	$	28,270	$	11,679	$	11,343
Investment Advisors	9,480		9,743		1,547		1,489
Institutional Investors	1,921		2,514		674		765
Investment Managers	3,071		5,090		1,461		1,468
Investments in New Businesses	461		560		1,350		1,273
Total from business segments	$	41,012	$	46,177	$	16,711	$	16,338
Corporate Overhead	445		1,368		339		485
	$	41,457	$	47,545	$	17,050	$	16,823



	Amortization
	2013		2012
Private Banks	$	16,497	$	17,139
Investment Advisors	6,063		5,305
Institutional Investors	937		906
Investment Managers	626		603
Investments in New Businesses	1,204		905
Total from business segments	$	25,327	$	24,858
Corporate Overhead	171		555
	$	25,498	$	25,413

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

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+ Details

Income Taxes

9 Months Ended

Sep. 30, 2013

Income Tax Disclosure [Abstract]

Income Taxes

The gross liability for unrecognized tax benefits at September 30, 2013 and December 31, 2012 was $12,731 and $11,553, respectively, exclusive of interest and penalties, of which $10,608 and $9,965 would affect the effective tax rate if the Company were to recognize the tax benefit.

The Company classifies interest and penalties on unrecognized tax benefits as income tax expense. As of September 30, 2013 and December 31, 2012, the combined amount of accrued interest and penalties related to tax positions taken on tax returns was $957 and $770, respectively.



	September 30, 2013		December 31, 2012
Gross liability for unrecognized tax benefits, exclusive of interest and penalties	$	12,731	$	11,553
Interest and penalties on unrecognized benefits	957		770
Total gross uncertain tax positions	$	13,688	$	12,323
Amount included in Current liabilities	$	4,985	$	5,291
Amount included in Other long-term liabilities	8,703		7,032
	$	13,688	$	12,323

The Company’s effective tax rates were 28.5 percent and 39.0 percent for the three months ended September 30, 2013 and 2012, respectively. For the nine months ended September 30, 2013 and 2012, the Company's tax rates were 33.3 percent and 37.6 percent, respectively. The third quarter 2013 tax rate was benefited by Pennsylvania tax law changes enacted on July 18, 2013 which become effective on January 1, 2014. The most significant changes affecting the Company’s tax rate were an increase in the annual utilization cap of the net operating loss deduction and the state apportionment of sales of services. The bill adopts a market-based approach for the sales apportionment factor that requires a company’s sales be recognized, for tax purposes, in the state the client benefits from such services. Under the current method, the sales apportionment factor is recognized in the state where the cost was incurred to perform those services. This change significantly reduced the apportionment to Pennsylvania which resulted in a reduction in the Company’s deferred tax liability. Accounting rules require the effect of changes to tax laws be recognized in the period in which the change occurred. The 2012 third quarter tax rate includes the U.S. deferred taxes on the undistributed earnings of SEI AK. As a result of the sale of SEI AK, the Company no longer considered the undistributed earnings of the subsidiary to be indefinitely reinvested and, therefore, accrued U.S deferred taxes on the cumulative undistributed earnings. This increase of taxes was partially offset by state tax planning occurring in the third quarter.

The 2013 tax rate was benefited by the reinstatement of the research and development tax credit. On January 2, 2013, President Barack Obama signed into law the American Taxpayer Relief Act of 2012 (the Act), which reinstated the research and development credit retroactively from January 1, 2012 through December 31, 2013. The accounting rules require the determination of current and deferred taxes be based upon the provisions of the enacted tax law as of the balance sheet date. Since the Act was not signed into law until January 2, 2013, the effect was not reflected in the tax provision for 2012. The effect of the 2012 research and development tax credit was therefore reflected in the 2013 tax rate. The 2013 tax rate was also benefited by the approval by Joint Tax Committee on certain refund requests. These benefits were partially offset by additional foreign taxes caused by the sale of SEI AK (See Note 13).

The Company files income tax returns in the United States on a consolidated basis and in many U.S. state and foreign jurisdictions. The Company is subject to examination of income tax returns by the Internal Revenue Service (IRS) and other domestic and foreign tax authorities. The Company is no longer subject to U.S. federal income tax examination for years before 2010 and is no longer subject to state, local or foreign income tax examinations by authorities for years before 2006.

The Company estimates it will recognize $4,985 of unrecognized tax benefits within the next twelve months due to the expiration of the statute of limitations and resolution of income tax audits. These unrecognized tax benefits are related to tax positions taken on certain federal, state, and foreign tax returns. However, the timing of the resolution of income tax examinations is highly uncertain, and the amounts ultimately paid, if any, upon resolution of the issues raised by the taxing authorities may differ materially from the amounts accrued for each year. While it is reasonably possible that some issues under examination could be resolved in the next twelve months, based upon the current facts and circumstances, the Company cannot reasonably estimate the timing of such resolution or total range of potential changes as it relates to the current unrecognized tax benefits that are recorded as part of the Company’s financial statements.

Commitments And Contingencies	9 Months Ended
Commitments And Contingencies	Sep. 30, 2013
Commitments and Contingencies Disclosure [Abstract]
Commitments And Contingencies	Commitments and Contingencies In the normal course of business, the Company is party to various claims and legal proceedings. One of SEI's principal subsidiaries, SIDCO, has been named as a defendant in certain putative class action complaints (the Complaints) related to leveraged exchange traded funds (ETFs) advised by ProShares Advisors, LLC. The first complaint was filed on August 5, 2009 and the subsequent cases were all consolidated in the Southern District of New York. The Complaints are purportedly made on behalf of all persons that purchased or otherwise acquired shares in various ProShares leveraged ETFs pursuant or traceable to allegedly false and misleading registration statements, prospectuses and statements of additional information. The Complaints name as defendants ProShares Advisors, LLC; ProShares Trust; ProShares Trust II, SIDCO, and various officers and trustees to ProShares Advisors, LLC; ProShares Trust and ProShares Trust II. The Complaints allege that SIDCO was the distributor and principal underwriter for the various ProShares leveraged ETFs that were distributed to authorized participants and ultimately shareholders. The Complaints allege that the registration statements for the ProShares ETFs were materially false and misleading because they failed adequately to describe the nature and risks of the investments and claim that SIDCO is liable for these purportedly material misstatements and omissions under Section 11 of the Securities Act of 1933. On September 7, 2012, the District Court for the Southern District of New York issued an opinion dismissing with prejudice the plaintiffs' amended complaint. Plaintiffs filed with the Second Circuit Court of Appeals a notice of appeal of the District Court's decision and on July 22, 2013, the Second Circuit Court of Appeals issued an opinion affirming the decision of the District Court dismissing the amended complaint. While the outcome of this litigation is uncertain given its early phase, SEI believes that it has valid defenses to plaintiffs' claims and intends to defend the lawsuits vigorously. SEI has been named in six lawsuits filed in Louisiana. Five lawsuits were filed in the 19th Judicial District Court for the Parish of East Baton Rouge, State of Louisiana. One of the five actions purports to set forth claims on behalf of a class and also names SPTC as a defendant and, as described below, was certified as a class in December 2012. Two of the other actions also name SPTC as a defendant. All five actions name various defendants in addition to SEI, and, in all five actions, the plaintiffs purport to bring a cause of action against SEI and SPTC under the Louisiana Securities Act. The class action originally included a claim against SEI and SPTC for an alleged violation of the Louisiana Unfair Trade Practices Act. Two of the other five actions include claims for violations of the Louisiana Racketeering Act and possibly conspiracy. In addition, another group of plaintiffs filed a lawsuit in the 23rd Judicial District Court for the Parish of Ascension, State of Louisiana, against SEI and SPTC and other defendants asserting claims of negligence, breach of contract, breach of fiduciary duty, violations of the uniform fiduciaries law, negligent misrepresentation, detrimental reliance, violations of the Louisiana Securities Act and Louisiana Racketeering Act and conspiracy. The underlying allegations in all the actions are purportedly related to the role of SPTC in providing back-office services to Stanford Trust Company. The petitions allege that SEI and SPTC aided and abetted or otherwise participated in the sale of “certificates of deposit” issued by Stanford International Bank. Two of the five actions filed in East Baton Rouge were removed to federal court and transferred by the Judicial Panel on Multidistrict Litigation to United States District Court for the Northern District of Texas. On August 31, 2011, the United States District Court for the Northern District of Texas issued an order and judgment that the causes of action alleged against SEI in the two removed actions were preempted by federal law and the court dismissed these cases with prejudice. Plaintiffs appealed this ruling, and on March 19, 2012, a panel of the Court of Appeals for the Fifth Circuit reversed the decision of the United States District Court and remanded the actions for further proceedings. On July 18, 2012, SEI filed a petition for a writ of certiorari in the United States Supreme Court, seeking review of the decision by the United States Court of Appeals in the Fifth Circuit to permit the claims against SEI to proceed. SEI believes that the trial court correctly concluded that the claims against SEI were barred by the federal Securities Litigation Uniform Standards Act and is requesting that the Supreme Court reinstate that dismissal. On January 18, 2013, the Supreme Court granted the petition for a writ of certiorari. On October 7, 2013, the Supreme Court heard oral argument on the appeal. The case filed in Ascension was also removed to federal court and transferred by the Judicial Panel on Multidistrict Litigation to the Northern District of Texas. The schedule for responding to that complaint has not yet been established. The plaintiffs in the remaining two cases in East Baton Rouge have granted SEI and SPTC an extension to respond to the filings. SEI and SPTC filed exceptions in the class action pending in East Baton Rouge, which the Court granted in part and dismissed the claims under the Louisiana Unfair Trade Practices Act and denied in part as to the other exceptions. SEI and SPTC filed an answer to the East Baton Rouge class action, plaintiffs filed a motion for class certification; and SEI and SPTC also filed a motion for summary judgment against certain named plaintiffs which the Court stated will not be set for hearing until after the hearing on the class certification motion. The Court in the East Baton Rouge action held a hearing on class certification on September 20, 2012. By oral decision on December 5, 2012 and later entered in a judgment signed on December 17, 2012 that was subsequently amended, the Court in East Baton Rouge certified a class to be composed of persons who purchased any Stanford International Bank certificates of deposit (SIB CDs) in Louisiana between January 1, 2007 and February 13, 2009; persons who renewed any SIB CD in Louisiana between January 1, 2007 and February 13, 2009; or any person for whom the Stanford Trust Company purchased SIB CDs in Louisiana between January 1, 2007 and February 13, 2009. On January 30, 2013, SEI and SPTC filed motions for appeal from the judgments that stated SEI's and SPTC's intention to move to stay the litigation. On February 1, 2013, plaintiffs filed a motion for Leave to File First Amended and Restated Class Action Petition in which they ask the Court to allow them to amend the petition in this case to add additional facts that were developed during discovery and adding claims against certain of SEI's insurance carriers. On February 5, 2013, the Court granted two of the motions for appeal and the motion for leave to amend. On February 15, 2013, SEI filed a motion for new trial, or, in the alternative, for reconsideration of the Court's order allowing amendment. On February 22, 2013, SEI filed a motion to stay proceedings in view of the pending Supreme Court case. On February 28, 2013, SEI responded to the First Amended and Restated Class Action Petition by filing an exception. On March 11, 2013, the insurance carrier defendants filed a notice of removal removing the case to the Middle District of Louisiana and on March 18, 2013, the insurance carrier defendants filed answers. On March 13, 2013, SEI notified the Judicial Panel on Multidistrict Litigation (MDL) of this case as a potential tag-along action. On March 19, 2013, plaintiffs filed a motion to remand, a motion for expedited briefing schedule, expedited status conference and expedited consideration of their motion to remand, a motion for leave to file under seal and a motion for order pursuant to 28 U.S.C. 1447(b) requiring removing defendants to supplement federal court record with certified copy of state court record. These motions are now fully briefed. On March 25, 2013, SEI filed a motion that the court decline to adopt the state court's order regarding class certification, which the court dismissed without prejudice to renew upon a determination of removal jurisdiction in an April 12, 2013 order that also dismissed without prejudice a motion to dismiss for lack of jurisdiction and improper venue filed on April 9, 2013 by one of the insurers. On April 1, 2013, the Louisiana Office of Financial Institutions (OFI) filed a motion to remand and sever claims, and a response to that motion by the insurers and opposition to that motion by the plaintiffs were filed on April 22, 2013. Along with the briefing in the Middle District of Louisiana, on March 13, 2013, SEI notified the Judicial Panel on Multidistrict Litigation (MDL) of this case as a potential tag-along action. On March 19, 2013, plaintiffs notified the MDL that they had filed a motion to remand and asked the panel to decline to issue a conditional transfer order. On March 29, 2013, the MDL issued a conditional transfer order (CTO). On April 18, 2013, OFI filed a motion to vacate the CTO or, in the alternative, stay any ruling to transfer the matter until after the Middle District of Louisiana ruled on OFI's motion to remand and sever. Plaintiffs filed a motion to vacate the CTO on April 19, 2013. SEI's responses to those motions were filed on May 9, 2013. On June 12, 2013, the MDL Panel issued an order notifying the parties that on July 25, 2013, it would consider, without oral argument, Plaintiffs' and OFI's motions to vacate the CTO. On August 7, 2013, the MDL Panel affirmed the CTO and transferred the matter against SEI to the US District Court for the Northern District of Texas; the MDL Panel also severed the claims against OFI and remanded those claims to the Middle District of Louisiana. On September 11, 2013, defendants filed a motion requesting a status conference with the Court to address the status of all pending motions. On October 4, 2013, Plaintiffs filed a petition for a writ of mandamus asking the United States Court of Appeals for the Fifth Circuit to review the MDL Panel’s transfer Order. While the outcome of this litigation is uncertain given its early phase, SEI and SPTC believe that they have valid defenses to plaintiffs' claims and intend to defend the lawsuits vigorously. Because of the uncertainty of the make-up of the classes, the outcome of the proceeding in the United States Supreme Court, the specific theories of liability that may survive a motion for summary judgment or other dispositive motion, the lack of discovery regarding damages, causation, mitigation and other aspects that may ultimately bear upon loss, the Company is not reasonably able to provide an estimate of loss, if any, with respect to the foregoing lawsuits.

Sale of SEI Asset Korea

9 Months Ended

Sep. 30, 2013

Disposal Group, Not Discontinued Operation, Disposal Disclosures [Abstract]

Sale of SEI Asset Korea

On July 31, 2012, the Company, MetLife International Holdings, Inc. (MetLife) and International Finance Corporation (IFC) entered into a definitive agreement with Baring Asset Management Limited to sell all ownership interest in SEI Asset Korea (SEI AK). SEI AK was located in South Korea and provided domestic equity and fixed income investment management services to financial institutions and pension funds.

On March 28, 2013, all conditions subject to closing the transaction were satisfied and all ownership interests in SEI AK were transferred to Barings Asset Management Limited. Under the terms of the agreement, a portion of the purchase price was paid upon closing with up to an additional $11,220 payable to the Company as a contingent purchase price with respect to three one-year periods ending on December 31, 2013, 2014, and 2015 depending upon whether SEI AK achieves specified revenue measures during such periods. Also, the net working capital of SEI AK at closing in excess of required regulatory capital, and subject to certain other adjustments, was distributed to the Company, MetLife and IFC in accordance with the ownership interests. Without regard to the contingent purchase price, the Company recognized a gain of $22.1 million, or $0.08 diluted earnings per share, during the nine months ended September 30, 2013 as a result of the sale. The Company's gain from the sale of SEI AK is included in Gain on sale of subsidiary on the accompanying Consolidated Statement of Operations.

Excluding the contingent purchase price, the Company received gross proceeds of $56,879 from the sale. The Company incurred $2,545 in transaction costs during the nine months ended September 30, 2013 for net proceeds of $54,334 resulting from the sale. The net effect of the cash received from the sale and the transfer of cash balances to the owners is reflected in Sale of subsidiary, net of cash transferred in the investing section of the Consolidated Statement of Cash flows.

The Company's ownership interest in SEI AK was 56.1 percent. The Company consolidated the assets, liabilities and operations of SEI AK in its Consolidated Financial Statements. As of December 31, 2012, SEI AK had total corporate assets of $54,783, of which $48,306 was included in Cash and cash equivalents on the Consolidated Balance Sheet. All other accounts of SEI AK were not material to any financial statement line item in the Consolidated Financial Statements. The ownership interests in SEI AK of MetLife and IFC were reflected in Noncontrolling interest in the Consolidated Financial Statements.

The operating results of SEI AK were included in the Private Banks business segment. SEI AK revenues and net income included in the Company's Consolidated Statement of Operations were as follows:



	For the Period January 1, 2013 through March 28, 2013
				For the Three Months Ended September 30, 2012			For the Nine Months Ended September 30, 2012


Revenues	$	2,889		$	2,779		$	8,632

Net income	$	796		$	729		$	1,817
Less: Income attributable to the noncontrolling interests	(350		)	(343		)	(797		)
Net income attributable to SEI AK	$	446		$	386		$	1,020

- Definition

The entire disclosure for the facts and circumstances leading to the completed or expected disposal, manner and timing of disposal, the gain (loss) recognized in the income statement and the income statement caption that includes that gain (loss), amounts of revenues and pretax profit or loss reported in discontinued operations, the segment in which the disposal group was reported, and the classification (whether sold or classified as held for sale) and carrying value of the assets and liabilities comprising the disposal group. Includes all disposal groups, including those classified as components of the entity (discontinued operations).

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+ Details

Settlement Agreement	9 Months Ended
Settlement Agreement	Sep. 30, 2013
Litigation Settlement [Abstract]
Settlement Agreement	Settlement Agreement On April 24, 2013, the Company entered into a Settlement Agreement with respect to litigation captioned Abu Dhabi Commercial Bank, et. al. v. Morgan Stanley & Co., Incorporated, et. al., brought by a group of plaintiffs, including the Company, related to the purchase of securities by the Company and others of Cheyne Finance LLC, a SIV security. In accordance with the Settlement Agreement, the Company received a cash settlement payment of $43,429 after fees and expenses during the three months ended June 30, 2013. The income related to the cash settlement payment is reflected in Other income on the accompanying Consolidated Statements of Operations.

Summary Of Significant Accounting Policies (Policy)

9 Months Ended

Sep. 30, 2013

Accounting Policies [Abstract]

Nature Of Operations

Nature of Operations

Basis Of Presentation

Basis of Presentation

Earnings Per Share

Earnings per Share

The calculations of basic and diluted earnings per share for the three months ended September 30, 2013 and 2012 are:



	For the Three Months Ended September 30, 2013
	Income (Numerator)		Shares (Denominator)	Per Share Amount
Basic earnings per common share	$	67,195	171,308	$	0.39
Dilutive effect of stock options	—		4,735
Diluted earnings per common share	$	67,195	176,043	$	0.38



	For the Three Months Ended September 30, 2012
	Income (Numerator)		Shares (Denominator)	Per Share Amount
Basic earnings per common share	$	50,743	173,429	$	0.29
Dilutive effect of stock options	—		1,940
Diluted earnings per common share	$	50,743	175,369	$	0.29



	For the Nine Months Ended September 30, 2013
	Income (Numerator)		Shares (Denominator)	Per Share Amount
Basic earnings per common share	$	222,609	172,043	$	1.29
Dilutive effect of stock options	—		3,993
Diluted earnings per common share	$	222,609	176,036	$	1.26



	For the Nine Months Ended September 30, 2012
	Income (Numerator)		Shares (Denominator)	Per Share Amount
Basic earnings per common share	$	150,263	174,869	$	0.86
Dilutive effect of stock options	—		1,448
Diluted earnings per common share	$	150,263	176,317	$	0.85

Cash and Cash Equivalents

Statements of Cash Flows

For purposes of the Consolidated Statements of Cash Flows, the Company considers investment instruments purchased with an original maturity of three months or less to be cash equivalents.

Reclassifications

Certain prior year amounts have been reclassified to conform to current year presentation.

Equity Method Investments

The Company accounts for its interest in LSV using the equity method because of its less than 50 percent ownership. The Company’s interest in the net assets of LSV is reflected in Investment in unconsolidated affiliates on the accompanying Consolidated Balance Sheets and its interest in the earnings of LSV is reflected in Equity in earnings of unconsolidated affiliates on the accompanying Consolidated Statements of Operations.

Variable Interest Entities

The Company does not have a significant equity investment in any of the VIEs and does not have an obligation to enter into any guarantee agreements with the VIEs. The Company is not the primary beneficiary of the VIEs because the expected fees and the expected return on any investment into the VIE by the Company relative to the expected returns of the VIE to the equity investor holders does not approach 50 percent of the expected losses or gains of the VIEs. Therefore, the Company is not required to consolidate any investment products that are VIEs into its financial statements. The Company’s variable interest in the VIEs, which consists of management fees and in some situations, seed capital, is not considered a significant variable interest.

The risks to the Company associated with its involvement with any of the investment products that are VIEs are limited to the cash flows received from the revenue generated for asset management, administration and distribution services and any equity investments in the VIEs. Both of these items are not significant. The Company has no other financial obligation to the VIEs.

Amounts relating to fees due from the VIEs included in Receivables and amounts relating to equity investments in the VIEs included in Investments Available for Sale on the Company’s Consolidated Balance Sheets are not significant to the total assets of the Company.

Fair Value of Financial Instruments

Available-for-sale Securities

These net unrealized gains are reported as a separate component of Accumulated other comprehensive income on the accompanying Consolidated Balance Sheets.

Trading Securities

Securities Owned

Summary Of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2013

Accounting Policies [Abstract]

Calculation Of Basic And Diluted Earnings Per Share

The calculations of basic and diluted earnings per share for the three months ended September 30, 2013 and 2012 are:



	For the Three Months Ended September 30, 2013
	Income (Numerator)		Shares (Denominator)	Per Share Amount
Basic earnings per common share	$	67,195	171,308	$	0.39
Dilutive effect of stock options	—		4,735
Diluted earnings per common share	$	67,195	176,043	$	0.38



	For the Three Months Ended September 30, 2012
	Income (Numerator)		Shares (Denominator)	Per Share Amount
Basic earnings per common share	$	50,743	173,429	$	0.29
Dilutive effect of stock options	—		1,940
Diluted earnings per common share	$	50,743	175,369	$	0.29



	For the Nine Months Ended September 30, 2013
	Income (Numerator)		Shares (Denominator)	Per Share Amount
Basic earnings per common share	$	222,609	172,043	$	1.29
Dilutive effect of stock options	—		3,993
Diluted earnings per common share	$	222,609	176,036	$	1.26



	For the Nine Months Ended September 30, 2012
	Income (Numerator)		Shares (Denominator)	Per Share Amount
Basic earnings per common share	$	150,263	174,869	$	0.86
Dilutive effect of stock options	—		1,448
Diluted earnings per common share	$	150,263	176,317	$	0.85

Adjustments To Reconcile Net Income To Net Cash Provided By Operating Activities

The following table provides the details of the adjustments to reconcile net income to net cash provided by operating activities for the nine months ended September 30:



	2013			2012
Net income	$	222,959		$	151,060
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	17,050			16,823
Amortization	25,498			25,413
Equity in earnings of unconsolidated affiliates	(86,204		)	(74,970		)
Distributions received from unconsolidated affiliate	109,173			72,306
Stock-based compensation	26,997			11,777
Provision for losses on receivables	(180		)	(112		)
Deferred income tax expense	(21,443		)	2,117
Gain from sale of SEI AK (See Note 13)	(22,112		)	—
Net gain from investments	(638		)	(7,577		)
Change in other long-term liabilities	1,671			2,803
Change in other assets	80			(1,063		)
Other	(4,199		)	4,759
Change in current asset and liabilities
Decrease (increase) in
Restricted cash for broker-dealer operations	500			—
Receivables from regulated investment companies	(8,495		)	(3,203		)
Receivables	(17,255		)	(54,995		)
Other current assets	(1,208		)	(863		)
Increase (decrease) in
Accounts payable	(3,960		)	1,568
Accrued liabilities	3,149			967
Deferred revenue	(1,088		)	(911		)
Total adjustments	17,336			(5,161		)
Net cash provided by operating activities	$	240,295		$	145,899

Investment In Unconsolidated Affiliates (Tables)

9 Months Ended

Sep. 30, 2013

Equity Method Investments and Joint Ventures [Abstract]

Condensed Statement Of Operations Of LSV

The following table contains the condensed statements of operations of LSV for the three and nine months ended September 30, 2013 and 2012:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2013		2012		2013		2012
Revenues	$	92,184	$	74,163	$	256,782	$	220,817
Net income	79,555		62,946		220,657		186,991

Composition Of Certain Financial Statement Captions (Tables)

9 Months Ended

Sep. 30, 2013

Items Included in Consolidated Statement of Financial Condition [Abstract]

Receivables

Receivables on the accompanying Consolidated Balance Sheets consist of:



	September 30, 2013			December 31, 2012
Trade receivables	$	46,855		$	46,650
Fees earned, not billed	126,943			116,019
Other receivables	13,209			9,870
	187,007			172,539
Less: Allowance for doubtful accounts	(625		)	(805		)
	$	186,382		$	171,734

Property And Equipment

Property and Equipment on the accompanying Consolidated Balance Sheets consists of:



	September 30, 2013			December 31, 2012
Buildings	$	138,106		$	137,751
Equipment	67,182			66,167
Land	9,929			9,929
Purchased software	95,448			91,468
Furniture and fixtures	16,909			18,535
Leasehold improvements	4,467			5,037
Construction in progress	1,106			112
	333,147			328,999
Less: Accumulated depreciation	(214,653		)	(201,418		)
Property and Equipment, net	$	118,494		$	127,581

Accrued Liabilities

Accrued liabilities on the accompanying Consolidated Balance Sheets consist of:



	September 30, 2013		December 31, 2012
Accrued employee compensation	$	55,729	$	63,996
Accrued employee benefits and other personnel	8,644		7,299
Accrued consulting, outsourcing and professional fees	21,606		16,676
Accrued brokerage fees	5,045		5,733
Accrued sub-advisory, distribution and other asset management fees	23,839		17,548
Accrued income taxes	26		104
Other accrued liabilities	21,750		26,949
Total accrued liabilities	$	136,639	$	138,305

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2013

Fair Value Disclosures [Abstract]

Fair Value Of Certain Financial Assets And Liabilities

The fair value of certain financial assets and liabilities of the Company was determined using the following inputs:



	At September 30, 2013
	Fair Value Measurements at Reporting Date Using
Assets	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Equity available-for-sale securities	$	10,644	$	10,644	$	—	$	—
Fixed income available-for-sale securities	75,542		—		75,542		—
Fixed income securities owned	20,728		—		20,728		—
Trading securities	4,841		4,841		—		—
	$	111,755	$	15,485	$	96,270	$	—



	At December 31, 2012
	Fair Value Measurements at Reporting Date Using
Assets	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Equity available-for-sale securities	$	15,926	$	15,926	$	—	$	—
Fixed income available-for-sale securities	59,943		—		59,943		—
Fixed income securities owned	20,088		—		20,088		—
Trading securities	5,909		4,706		—		1,203
	$	101,866	$	20,632	$	80,031	$	1,203

Reconciliation For All Assets And Liabilities Of The Company Measured At Fair Value On A Recurring Basis Using Significant Unobservable Inputs (Level 3)



	Trading Securities
Balance, January 1, 2013	$	1,203
Purchases	—
Issuances	—
Principal prepayments and settlements	(1,167		)
Sales	—
Total gains or (losses) (realized/unrealized):
Included in earnings	(36		)
Included in other comprehensive income	—
Transfers in and out of Level 3	—
Balance, September 30, 2013	$	—



	Trading Securities
Balance, January 1, 2012	$	52,623
Purchases	—
Issuances	—
Principal prepayments and settlements	(9,833		)
Sales	—
Total gains or (losses) (realized/unrealized):
Included in earnings	7,303
Included in other comprehensive income	—
Transfers in and out of Level 3	—
Balance, September 30, 2012	$	50,093

Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2013

Marketable Securities [Abstract]

Investments Available For Sale

Investments available for sale classified as non-current assets consist of:



	At September 30, 2013
	Cost Amount		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
SEI-sponsored mutual funds	$	7,148	$	873	$	—	$	8,021
Equities and other mutual funds	2,589		34		—		2,623
Debt securities	74,102		1,440		—		75,542
	$	83,839	$	2,347	$	—	$	86,186



	At December 31, 2012
	Cost Amount		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
SEI-sponsored mutual funds	$	12,953	$	376	$	(13	)	$	13,316
Equities and other mutual funds	2,610		—		—			2,610
Debt securities	55,923		4,020		—			59,943
	$	71,486	$	4,396	$	(13	)	$	75,869

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

Shareholders' Equity (Tables)

9 Months Ended

Sep. 30, 2013

Stockholders' Equity Note [Abstract]

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block]

The Company recognized stock-based compensation expense in its Consolidated Financial Statements in the three and nine months ended September 30, 2013 and 2012, respectively, as follows:



	Three Months Ended September 30,						Nine Months Ended September 30,
	2013			2012			2013			2012
Stock-based compensation expense	$	11,097		$	3,879		$	26,997		$	11,777
Less: Deferred tax benefit	(4,125		)	(1,573		)	(9,908		)	(4,381		)
Stock-based compensation expense, net of tax	$	6,972		$	2,306		$	17,089		$	7,396

Schedule Of Reconciliation Of Noncontrolling Interest On The Consolidated Balance Sheet

The following table provides a reconciliation of Noncontrolling interest on the Consolidated Balance Sheet for the period from January 1, 2013 to September 30, 2013:



	Noncontrolling interest
Balance, January 1, 2013	$	19,149
Net income attributable to noncontrolling interest	350
Foreign currency translation adjustments	(451		)
Sale of subsidiary (See Note 13)	(19,048		)
Balance, September 30, 2013	$	—

The following table provides a reconciliation of Noncontrolling interest on the Consolidated Balance Sheet for the period from January 1, 2012 to September 30, 2012:



	Noncontrolling interest
Balance, January 1, 2012	$	16,143
Net income attributable to noncontrolling interest	797
Foreign currency translation adjustments	833
Balance, September 30, 2012	$	17,773

Accumulated Comprehensive Income (Loss) (Tables)

9 Months Ended

Sep. 30, 2013

Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]

Schedule Of Accumulated Other Comprehensive Income (Loss), Net Of Tax

Accumulated other comprehensive income, net of tax, consists of:



	Foreign Currency Translation Adjustments			Unrealized Holding Gains (Losses) on Investments			Accumulated Other Comprehensive (Loss) Income
Total accumulated comprehensive income at December 31, 2012	$	3,861		$	2,829		$	6,690
Less: Total accumulated comprehensive income attributable to noncontrolling interest at December 31, 2012	(451		)	—			(451		)
Total accumulated comprehensive income attributable to SEI Investments Company at December 31, 2012	$	3,410		$	2,829		$	6,239

Total comprehensive loss for the nine months ended September 30, 2013	$	(3,961	)	$	(1,173	)	$	(5,134	)
Less: Total comprehensive loss attributable to noncontrolling interest for the nine months ended September 30, 2013	451			—			451
Total comprehensive loss attributable to SEI Investments Company for the nine months ended September 30, 2013	$	(3,510	)	$	(1,173	)	$	(4,683	)

Total accumulated comprehensive income at September 30, 2013	$	(100	)	$	1,656		$	1,556
Less: Total accumulated comprehensive income attributable to noncontrolling interest at September 30, 2013	—			—			—
Total accumulated comprehensive income attributable to SEI Investments Company at September 30, 2013	$	(100	)	$	1,656		$	1,556

Business Segment Information (Tables)

9 Months Ended

Sep. 30, 2013

Segment Reporting Information [Line Items]

Schedule Of Financial Information About Business Segments

The following tables highlight certain unaudited financial information about each of the Company’s business segments for the nine months ended September 30, 2013 and 2012.



	Private Banks		Investment Advisors		Institutional Investors		Investment Managers		Investments In New Businesses			Total
	For the Nine Months Ended September 30, 2013
Revenues	$	291,258	$	175,868	$	190,385	$	166,542	$	3,055		$	827,108
Expenses	289,632		98,291		97,595		109,432		11,774			606,724
Operating profit (loss)	$	1,626	$	77,577	$	92,790	$	57,110	$	(8,719	)	$	220,384
Gain on sale of subsidiary	22,112		—		—		—		—			22,112
Total profit (loss)	$	23,738	$	77,577	$	92,790	$	57,110	$	(8,719	)	$	242,496



	Private Banks		Investment Advisors		Institutional Investors		Investment Managers		Investments In New Businesses			Total
	For the Nine Months Ended September 30, 2012
Revenues	$	268,367	$	150,227	$	167,293	$	142,235	$	2,765		$	730,887
Expenses	263,612		88,440		86,494		92,711		11,080			542,337
Operating profit (loss)	$	4,755	$	61,787	$	80,799	$	49,524	$	(8,315	)	$	188,550

The following tables highlight certain unaudited financial information about each of the Company’s business segments for the three months ended September 30, 2013 and 2012.



	Private Banks		Investment Advisors		Institutional Investors		Investment Managers		Investments In New Businesses			Total
	For the Three Months Ended September 30, 2013
Revenues	$	97,370	$	61,393	$	63,539	$	57,266	$	1,087		$	280,655
Expenses	95,579		33,768		33,058		37,763		4,146			204,314
Operating profit (loss)	$	1,791	$	27,625	$	30,481	$	19,503	$	(3,059	)	$	76,341



	Private Banks		Investment Advisors		Institutional Investors		Investment Managers		Investments In New Businesses			Total
	For the Three Months Ended September 30, 2012
Revenues	$	92,076	$	51,384	$	58,081	$	49,311	$	900		$	251,752
Expenses	91,209		30,114		29,654		32,122		3,698			186,797
Operating profit (loss)	$	867	$	21,270	$	28,427	$	17,189	$	(2,798	)	$	64,955

Reconciliation Of Total Operating Profit Reported For Business Segments To Income From Operations In Consolidated Statements Of Operations



	2013			2012
Total operating profit from segments above	$	220,384		$	188,550
Corporate overhead expenses	(40,719		)	(33,830		)
Noncontrolling interest reflected in segments	289			657
Income from operations	$	179,954		$	155,377



	2013			2012
Total operating profit from segments above	$	76,341		$	64,955
Corporate overhead expenses	(14,402		)	(11,668		)
Noncontrolling interest reflected in segments	—			203
Income from operations	$	61,939		$	53,490

Reconciliation of Other Significant Reconciling Items from Segments to Consolidated [Table Text Block]

The following tables provide additional information for the nine months ended September 30, 2013 and 2012 pertaining to our business segments:



	Capital Expenditures				Depreciation
	2013		2012		2013		2012
Private Banks	$	26,079	$	28,270	$	11,679	$	11,343
Investment Advisors	9,480		9,743		1,547		1,489
Institutional Investors	1,921		2,514		674		765
Investment Managers	3,071		5,090		1,461		1,468
Investments in New Businesses	461		560		1,350		1,273
Total from business segments	$	41,012	$	46,177	$	16,711	$	16,338
Corporate Overhead	445		1,368		339		485
	$	41,457	$	47,545	$	17,050	$	16,823



	Amortization
	2013		2012
Private Banks	$	16,497	$	17,139
Investment Advisors	6,063		5,305
Institutional Investors	937		906
Investment Managers	626		603
Investments in New Businesses	1,204		905
Total from business segments	$	25,327	$	24,858
Corporate Overhead	171		555
	$	25,498	$	25,413

The following tables provide additional information for the three months ended September 30, 2013 and 2012 pertaining to our business segments:



	Capital Expenditures				Depreciation
	2013		2012		2013		2012
Private Banks	$	9,376	$	8,248	$	3,799	$	3,911
Investment Advisors	3,513		2,797		521		503
Institutional Investors	777		647		222		252
Investment Managers	1,596		927		525		500
Investments in New Businesses	186		140		442		449
Total from business segments	$	15,448	$	12,759	$	5,509	$	5,615
Corporate overhead	259		228		107		146
	$	15,707	$	12,987	$	5,616	$	5,761



	Amortization
	2013		2012
Private Banks	$	5,704	$	7,660
Investment Advisors	2,105		1,832
Institutional Investors	326		302
Investment Managers	218		201
Investments in New Businesses	419		332
Total from business segments	$	8,772	$	10,327
Corporate overhead	57		57
	$	8,829	$	10,384

Income Taxes (Tables)

9 Months Ended

Sep. 30, 2013

Income Tax Disclosure [Abstract]

Schedule Of Interest And Penalties



	September 30, 2013		December 31, 2012
Gross liability for unrecognized tax benefits, exclusive of interest and penalties	$	12,731	$	11,553
Interest and penalties on unrecognized benefits	957		770
Total gross uncertain tax positions	$	13,688	$	12,323
Amount included in Current liabilities	$	4,985	$	5,291
Amount included in Other long-term liabilities	8,703		7,032
	$	13,688	$	12,323

Sale of SEI Asset Korea Sale of SEI Asset Korea (Tables)

9 Months Ended

Sep. 30, 2013

Disposal Group, Not Discontinued Operation, Disposal Disclosures [Abstract]

Schedule of Disposal Groups, Including Discontinued Operations, Income Statement, Balance Sheet and Additional Disclosures [Table Text Block]

SEI AK revenues and net income included in the Company's Consolidated Statement of Operations were as follows:



	For the Period January 1, 2013 through March 28, 2013
				For the Three Months Ended September 30, 2012			For the Nine Months Ended September 30, 2012


Revenues	$	2,889		$	2,779		$	8,632

Net income	$	796		$	729		$	1,817
Less: Income attributable to the noncontrolling interests	(350		)	(343		)	(797		)
Net income attributable to SEI AK	$	446		$	386		$	1,020

- Definition

Tabular disclosure of disposal groups, which may include the gain (loss) recognized in the income statement and the income statement caption that includes that gain (loss), amounts of revenues and pretax profit or loss reported in discontinued operations, the classification and carrying value of the assets and liabilities comprising the disposal group, and the segment in which the disposal group was reported. Also may include the amount of adjustments to amounts previously reported in discontinued operations such as resolution of contingencies arising from the disposal transaction or the operations of the component prior to disposal.

+ References + Details

Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2013	Mar. 28, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Cash and cash equivalents	$ 527,214		$ 397,677	$ 527,214	$ 397,677	$ 452,247	$ 420,986
Payments to acquire software				$ 31,044	25,894
Capitalized software weighted average remaining life	8 years 9 months			8 years 9 months
Amortization expense related to capitalized software				$ 25,328	$ 24,858
Capitalized software, accumulated amortization	$ 171,015			$ 171,015		149,747
Anti-dilutive employee stock options	3,042,000		9,552,000	5,522,000	13,908,000
Antidilutive securities excluded from computation of net income, per outstanding unit, amount	$ 31.39		$ 26.51	$ 29.22	$ 23.40
SEI-Sponsored Open-Ended Money Market Mutual Funds [Member]
Cash and cash equivalents	$ 368,819			$ 368,819		247,314
SEI Investments (Europe) Limited [Member]
Restricted cash	5,000			5,000		5,000
SEI Investments Distribution Co. (SIDCO) [Member]
Restricted cash	$ 500			$ 500		1,000
SEI Wealth Platform [Member]
Capitalized software weighted average remaining life	8 years 9 months			8 years 9 months
Amortization expense related to capitalized software				$ 25,046	$ 24,506
Net book value of SWP	$ 307,121			307,121
Capitalized software, accumulated amortization	140,925			140,925
Capitalized software development costs in-progress associated with future releases	$ 5,943			$ 5,943
Software development cost useful life				15 years
Accelerated amortization for SWP abandoned components					$ 2,661
SEI Asset Korea Co., Ltd. [Member]
Percentage of ownership before sale of subsidiary		56.10%
Closing date, sale of subsidiary				Mar. 28, 2013
Cash and cash equivalents						$ 48,306

Summary Of Significant Accounting Policies (Calculation Of Basic And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Accounting Policies [Abstract]
Basic earnings per common share, Income (Numerator)	$ 67,195	$ 50,743	$ 222,609	$ 150,263
Shares used to compute basic earnings per share	171,308	173,429	172,043	174,869
Basic earnings per common share	$ 0.39	$ 0.29	$ 1.29	$ 0.86
Dilutive effect of stock options, income	$ 0	$ 0	$ 0	$ 0
Dilutive effect of stock options, shares	4,735	1,940	3,993	1,448
Diluted earnings per common share, Income (Numerator)	$ 67,195	$ 50,743	$ 222,609	$ 150,263
Shares used to compute diluted earnings per share	176,043	175,369	176,036	176,317
Diluted earnings per common share	$ 0.38	$ 0.29	$ 1.26	$ 0.85

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References + Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Net Income
-URI http://asc.fasb.org/extlink&oid=6518256

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.19)
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.18)
-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.22)
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Other Comprehensive Income
-URI http://asc.fasb.org/extlink&oid=6519514

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=28358780&loc=d3e565-108580

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 19
-Article 5

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 20
-Article 9

+ Details

Summary Of Significant Accounting Policies (Adjustments To Reconcile Net Income To Net Cash Provided By Operating Activities) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Accounting Policies [Abstract]
Net income	$ 67,195	$ 51,086	$ 222,959	$ 151,060
Depreciation	5,616	5,761	17,050	16,823
Amortization	8,829	10,384	25,498	25,413
Equity in earnings of unconsolidated affiliates	(31,028)	(24,928)	(86,204)	(74,970)
Distributions received from unconsolidated affiliate			109,173	72,306
Stock-based compensation	11,097	3,879	26,997	11,777
Provision for losses on receivables			(180)	(112)
Deferred income tax expense			(21,443)	2,117
Gain on sale of SEI AK (See Note 13)	$ 0	$ 0	(22,112)	0
Net gain from investments			(638)	(7,577)
Change in other long-term liabilities			1,671	2,803
Change in other assets			80	(1,063)
Other			(4,199)	4,759
Decrease (increase) in restricted cash for broker-dealer operations			500	0
Decrease (increase) in receivables from regulated investment companies			(8,495)	(3,203)
Decrease (increase) in receivables			(17,255)	(54,995)
Decrease (increase) in other current assets			(1,208)	(863)
Increase (decrease) in Accounts payable			(3,960)	1,568
Increase (decrease) in Accrued liabilities			3,149	967
Increase (decrease) in Deferred revenue			(1,088)	(911)
Total adjustments			17,336	(5,161)
Net cash provided by operating activities			$ 240,295	$ 145,899

Investment In Unconsolidated Affiliates (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Oct. 22, 2013	Dec. 31, 2012	Oct. 02, 2012	Apr. 11, 2011
Investments in and Advances to Affiliates [Line Items]
Partnership distribution payments received from LSV			$ 109,173	$ 72,306
Company's share in the earnings of equity method investee	$ 31,028	$ 24,928	$ 86,204	74,970
LSV Employee Group II [Member]
Investments in and Advances to Affiliates [Line Items]
Originating transaction for Company's guaranty agreement			In April 2011, LSV Employee Group II agreed to purchase a partnership interest of an existing LSV employee
Purchase price paid for partnership interest in LSV								$ 4,300
Triggering event related to Company's guaranty agreement			The lenders have the right to seek payment from the Company in the event of a default by LSV Employee Group II
Loans Payable					$ 1,026
LSV Employee Group III [Member]
Investments in and Advances to Affiliates [Line Items]
Originating transaction for Company's guaranty agreement			In October 2012, LSV Employee Group III purchased a portion of the partnership interest of three existing LSV employees
Purchase price paid for partnership interest in LSV							$ 77,700
Loans Payable							69,930
Maximum [Member]
Investments in and Advances to Affiliates [Line Items]
Equity method investment, ownership percentage	50.00%		50.00%
Financial Guarantee [Member] \| L S V Asset Management [Member]
Investments in and Advances to Affiliates [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted					13,086		24,930
Financial Guarantee [Member] \| LSV Employee Group II [Member]
Investments in and Advances to Affiliates [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted								$ 3,655
Guarantor Obligations, Current Carrying Value					0
Financial Guarantee [Member] \| LSV Employee Group III [Member]
Investments in and Advances to Affiliates [Line Items]
Triggering event related to Company's guaranty agreement			The lenders have the right to seek payment from the Company in the event of a default by LSV Employee Group III
Guarantor Obligations, Maximum Exposure, Undiscounted					45,000		$ 45,000
Guarantor Obligations, Current Carrying Value					$ 0
L S V Asset Management [Member]
Investments in and Advances to Affiliates [Line Items]
Equity method investment, ownership percentage	39.30%		39.30%			39.80%
Total investment in equity method investee	$ 46,414		$ 46,414
Goodwill	3,062		3,062
Company's share in the earnings of equity method investee	31,285	$ 24,928	86,871	$ 74,970
Gao Fu [Member]
Investments in and Advances to Affiliates [Line Items]
Total investment in equity method investee	11,015		11,015
Company's share in the earnings of equity method investee	$ (257)		$ (667)

Investment In Unconsolidated Affiliates (Condensed Statement Of Operations Of LSV) (Details) - L S V Asset Management [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Summarized Financial Information, Revenue	$ 92,184	$ 74,163	$ 256,782	$ 220,817
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	$ 79,555	$ 62,946	$ 220,657	$ 186,991

Variable Interest Entities - Investment Products (Details)	9 Months Ended
	Sep. 30, 2013
Variable Interest Entity [Line Items]
Percentage not approached by expected return on any VIE investment	50.00%

Composition Of Certain Financial Statement Captions (Receivables) (Details) - USD ($) $ in Thousands	Sep. 30, 2013	Dec. 31, 2012
Items Included in Consolidated Statement of Financial Condition [Abstract]
Trade receivables	$ 46,855	$ 46,650
Fees earned, not billed	126,943	116,019
Other receivables	13,209	9,870
Gross receivables	187,007	172,539
Less: Allowance for doubtful accounts	(625)	(805)
Receivables, net	$ 186,382	$ 171,734

Composition Of Certain Financial Statement Captions (Property And Equipment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Items Included in Consolidated Statement of Financial Condition [Abstract]
Buildings	$ 138,106		$ 138,106		$ 137,751
Equipment	67,182		67,182		66,167
Land	9,929		9,929		9,929
Purchased software	95,448		95,448		91,468
Furniture and fixtures	16,909		16,909		18,535
Leasehold improvements	4,467		4,467		5,037
Construction in progress	1,106		1,106		112
Property and Equipment, gross	333,147		333,147		328,999
Less: Accumulated depreciation	(214,653)		(214,653)		(201,418)
Property and Equipment, net	118,494		118,494		$ 127,581
Depreciation expense	$ 5,616	$ 5,761	$ 17,050	$ 16,823

Composition Of Certain Financial Statement Captions (Accrued Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2013	Dec. 31, 2012
Items Included in Consolidated Statement of Financial Condition [Abstract]
Accrued employee compensation	$ 55,729	$ 63,996
Accrued employee benefits and other personnel	8,644	7,299
Accrued consulting, outsourcing and professional fees	21,606	16,676
Accrued brokerage fees	5,045	5,733
Accrued sub-advisory, distribution and other asset management fees	23,839	17,548
Accrued income taxes	26	104
Other accrued liabilities	21,750	26,949
Total accrued liabilities	$ 136,639	$ 138,305

Fair Value Measurements (Narrative) (Details) - USD ($)	9 Months Ended
Fair Value Measurements (Narrative) (Details) - USD ($)	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets	$ 111,755,000	$ 101,866,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	0
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets	0	1,203,000
Financial liabilities	$ 0	$ 0

Fair Value Measurements (Fair Value Of Certain Financial Assets And Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity available-for-sale securities	$ 10,644	$ 15,926
Fixed income available-for-sale securities	75,542	59,943
Fixed income securities owned	20,728	20,088
Trading securities	4,841	5,909
Assets, fair value	111,755	101,866
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity available-for-sale securities	10,644	15,926
Fixed income available-for-sale securities	0	0
Fixed income securities owned	0	0
Trading securities	4,841	4,706
Assets, fair value	15,485	20,632
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity available-for-sale securities	0	0
Fixed income available-for-sale securities	75,542	59,943
Fixed income securities owned	20,728	20,088
Trading securities	0	0
Assets, fair value	96,270	80,031
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity available-for-sale securities	0	0
Fixed income available-for-sale securities	0	0
Fixed income securities owned	0	0
Trading securities	0	1,203
Assets, fair value	$ 0	$ 1,203

Fair Value Measurements (Reconciliation For All Assets And Liabilities Of The Company Measured At Fair Value On A Recurring Basis Using Significant Unobservable Inputs (Level 3)) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance, January 1	$ 1,203	$ 52,623
Purchases	0	0
Issuances	0	0
Principal prepayments and settlements	(1,167)	(9,833)
Sales	0	0
Total gains or (losses) (realized/unrealized), Included in earnings	(36)	7,303
Total gains or (losses) (realized/unrealized), Included in other comprehensive income	0	0
Transfers in and out of Level 3	0	0
Ending balance	$ 0	$ 50,093

Marketable Securities (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
Marketable Securities (Narrative) (Details) - USD ($)	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Schedule of Investments [Line Items]
Net unrealized holding gains	$ 1,656,000		$ 1,656,000		$ 2,829,000
Unrealized holding gains during the period, income tax expense			691,000		1,554,000
Available-for-sale Securities, Gross Realized Gains			710,000	$ 0
Available-for-sale Securities, Gross Realized Losses			(261,000)	0
Trading securities	4,841,000		4,841,000		5,909,000
Securities owned	20,728,000		$ 20,728,000		20,088,000
SEI Private Trust Company [Member] \| Minimum [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Maturities, Date			Dec. 15, 2020
SEI Private Trust Company [Member] \| Maximum [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Maturities, Date			Mar. 20, 2043
U.S. Government Agency And Commercial Paper Securities [Member]
Schedule of Investments [Line Items]
Realized Investment Gains (Losses)	0	$ 0	$ 0	0
SIV Securities [Member]
Schedule of Investments [Line Items]
Trading Securities, Realized Gain (Loss)				7,343,000
LSV-Sponsored Mutual Funds [Member]
Schedule of Investments [Line Items]
Trading securities	4,841,000		4,841,000		$ 4,706,000
Trading Securities, Realized Gain (Loss)	$ 610,000	$ 357,000	$ 135,000	$ 520,000

Marketable Securities (Investments Available For Sale) (Details) - USD ($) $ in Thousands	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Investment Available for Sale, Cost Amount	$ 83,839	$ 71,486
Investment Available for Sale, Gross Unrealized Gains	2,347	4,396
Investment Available for Sale, Gross Unrealized Losses	0	13
Investment Available for Sale, Fair Value	86,186	75,869
SEI-Sponsored Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment Available for Sale, Cost Amount	7,148	12,953
Investment Available for Sale, Gross Unrealized Gains	873	376
Investment Available for Sale, Gross Unrealized Losses	0	13
Investment Available for Sale, Fair Value	8,021	13,316
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment Available for Sale, Cost Amount	2,589	2,610
Investment Available for Sale, Gross Unrealized Gains	34	0
Investment Available for Sale, Gross Unrealized Losses	0	0
Investment Available for Sale, Fair Value	2,623	2,610
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment Available for Sale, Cost Amount	74,102	55,923
Investment Available for Sale, Gross Unrealized Gains	1,440	4,020
Investment Available for Sale, Gross Unrealized Losses	0	0
Investment Available for Sale, Fair Value	$ 75,542	$ 59,943

- Definition

Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

+ References + Details

Lines Of Credit (Details) $ in Thousands	9 Months Ended
Lines Of Credit (Details) $ in Thousands	Sep. 30, 2013 USD ($)
Two Thousand Twelve Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Term	5 years
Credit facility maximum borrowing capacity	$ 300,000
Credit facility expiration date	Feb. 02, 2017
Credit facility variable interest rate basis spread	1.25%
Credit facility variable interest rate basis	LIBOR
Credit facility commitment fee per annum on daily unused portion	0.15%
Credit facility aggregate amount that may increase	$ 100,000
Credit facility covenant terms	The Credit Facility contains covenants that restrict the ability of the Company to engage in mergers, consolidations, asset sales, investments, transactions with affiliates, or to incur liens, as defined in the agreement. In the event of a default under the Credit Facility, the Company would also be restricted from paying dividends on, or repurchasing, its common stock without the approval of the lenders.
Credit facility amount outstanding	$ 0
Credit facility covenant compliance	The Company was in compliance with all covenants of the Credit Facility
Canadian Subsidiary [Member]
Line of Credit Facility [Line Items]
Credit facility maximum borrowing capacity	$ 2,000
Credit facility amount outstanding	$ 0
Credit facility covenant compliance	The Company was in compliance with all covenants of the Canadian Credit Facility

Shareholders' Equity (Narrative) (Details) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013 USD ($) $ / shares plans shares	Sep. 30, 2012 $ / shares	Sep. 30, 2013 USD ($) $ / shares shares	Sep. 30, 2012 USD ($) $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	$ 29,229		$ 29,229
Change in management estimate of stock based compensation expense amortization			13,440
Total intrinsic value of options exercised			37,171
Aggregate intrinsic value of options exercisable	$ 82,557		$ 82,557
Share Price \| $ / shares	$ 30.91		$ 30.91
Weighted average exercise price per share \| $ / shares	$ 18.54		$ 18.54
Total options that were outstanding \| shares	22,146,000		22,146,000
Total options that were exercisable \| shares	6,676,000		6,676,000
Shares purchased and retired \| shares			4,879,000
Company purchased, cost			$ 145,269
Remaining stock repurchase authorization amount			$ 45,744
Dividends declared per common share \| $ / shares	$ 0.00	$ 0.00	$ 0.20	$ 0.15
Dividends, Common Stock, Cash			$ 34,400	$ 26,117
2007 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of active equity compensation plans \| plans	1
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant \| shares	20,000,000		20,000,000
Vesting Rate When Specified Diluted Earnings Per Share Targets are Achieved	50.00%
Vesting Rate Higher Specified Diluted Earnings Per Share Targets are Achieved	50.00%

Shareholders' Equity (Stock-Based Compensation Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Stockholders' Equity Note [Abstract]
Stock-based compensation expense	$ 11,097	$ 3,879	$ 26,997	$ 11,777
Less: Deferred tax benefit	(4,125)	(1,573)	(9,908)	(4,381)
Stock-based compensation expense, net of tax	$ 6,972	$ 2,306	$ 17,089	$ 7,396

Shareholders' Equity (Schedule Of Reconciliation Of Noncontrolling Interest On The Consolidated Balance Sheet) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance	$ 19,149	$ 16,143
Net income attributable to the noncontrolling interest	350	797
Foreign currency translation adjustments	(451)	833
Noncontrolling Interest, Decrease from Deconsolidation	(19,048)
Ending balance	$ 0	$ 17,773

Accumulated Comprehensive Income (Loss) (Schedule Of Accumulated Other Comprehensive Income (Loss), Net Of Tax) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Accumulated other comprehensive income (loss), Foreign Currency Translation Adjustments	$ (100)		$ (100)		$ 3,410
Accumulated other comprehensive income (loss), Unrealized Holding Gains (Losses) on Investments	1,656		1,656		2,829
Accumulated Other Comprehensive Income (Loss)	1,556		1,556		6,239
Total comprehensive loss, Foreign Currency Translation Adjustments	3,146	$ 3,464	(3,961)	$ 4,011
Total comprehensive loss, Unrealized Holding Gains (Losses) on Investments			(1,173)
Total other comprehensive income (loss), net of tax	3,555	$ 4,060	(5,134)	4,626
Total comprehensive loss attributable to noncontrolling interest, Foreign Currency Translation Adjustments			451	$ (833)
Total comprehensive income attributable to noncontrolling interest, Unrealized Holding Gains (Losses) on Investments			0
Total comprehensive loss attributable to noncontrolling interest			451
Total comprehensive income attributable to SEI Investments Company, Foreign Currency Translation Adjustments			(3,510)
Total comprehensive (loss) attributable to SEI Investments Company, Unrealized Holding Gains (Losses) on Investments			(1,173)
Total comprehensive income attributable to SEI Investments Company			(4,683)
SEI Investments Company [Member]
Accumulated other comprehensive income (loss), Foreign Currency Translation Adjustments	(100)		(100)		3,861
Accumulated other comprehensive income (loss), Unrealized Holding Gains (Losses) on Investments	1,656		1,656		2,829
Accumulated Other Comprehensive Income (Loss)	1,556		1,556		6,690
Noncontrolling Interest [Member]
Accumulated other comprehensive income (loss), Foreign Currency Translation Adjustments	0		0		(451)
Accumulated other comprehensive income (loss), Unrealized Holding Gains (Losses) on Investments	0		0		0
Accumulated Other Comprehensive Income (Loss)	$ 0		$ 0		$ (451)

Business Segment Information (Schedule Of Financial Information About Business Segments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting Information [Line Items]
Revenues	$ 280,655	$ 251,752	$ 827,108	$ 730,887
Expenses	204,314	186,797	606,724	542,337
Gain on sale of subsidiary			22,112
Total profit (loss)			242,496
Private Banks [Member]
Segment Reporting Information [Line Items]
Revenues	97,370	92,076	291,258	268,367
Expenses	95,579	91,209	289,632	263,612
Operating profit (loss)	1,791	867	1,626	4,755
Gain on sale of subsidiary			22,112
Total profit (loss)			23,738
Investment Advisors [Member]
Segment Reporting Information [Line Items]
Revenues	61,393	51,384	175,868	150,227
Expenses	33,768	30,114	98,291	88,440
Operating profit (loss)	27,625	21,270	77,577	61,787
Gain on sale of subsidiary			0
Total profit (loss)			77,577
Institutional Investors [Member]
Segment Reporting Information [Line Items]
Revenues	63,539	58,081	190,385	167,293
Expenses	33,058	29,654	97,595	86,494
Operating profit (loss)	30,481	28,427	92,790	80,799
Gain on sale of subsidiary			0
Total profit (loss)			92,790
Investment Managers [Member]
Segment Reporting Information [Line Items]
Revenues	57,266	49,311	166,542	142,235
Expenses	37,763	32,122	109,432	92,711
Operating profit (loss)	19,503	17,189	57,110	49,524
Gain on sale of subsidiary			0
Total profit (loss)			57,110
Investments In New Businesses [Member]
Segment Reporting Information [Line Items]
Revenues	1,087	900	3,055	2,765
Expenses	4,146	3,698	11,774	11,080
Operating profit (loss)	(3,059)	(2,798)	(8,719)	(8,315)
Gain on sale of subsidiary			0
Total profit (loss)			(8,719)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating profit (loss)	$ 76,341	$ 64,955	$ 220,384	$ 188,550

Business Segment Information (Reconciliation Of Total Operating Profit Reported For Business Segments To Income From Operations In Consolidated Statements Of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Noncontrolling interest reflected in segments	$ 0	$ 343	$ 350	$ 797
Income from operations	61,939	53,490	179,954	155,377
Operating Segments [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total operating profit from segments above	76,341	64,955	220,384	188,550
Segment Reconciling Items [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Corporate overhead expenses	(14,402)	(11,668)	(40,719)	(33,830)
Noncontrolling interest reflected in segments	$ 0	$ (203)	$ (289)	$ (657)

Business Segment Information (Schedule Of Additional Information Pertaining To Business Segments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting Information [Line Items]
Capital Expenditures	$ 15,707	$ 12,987	$ 41,457	$ 47,545
Depreciation	5,616	5,761	17,050	16,823
Amortization	8,829	10,384	25,498	25,413
Private Banks [Member]
Segment Reporting Information [Line Items]
Capital Expenditures	9,376	8,248	26,079	28,270
Depreciation	3,799	3,911	11,679	11,343
Amortization	5,704	7,660	16,497	17,139
Investment Advisors [Member]
Segment Reporting Information [Line Items]
Capital Expenditures	3,513	2,797	9,480	9,743
Depreciation	521	503	1,547	1,489
Amortization	2,105	1,832	6,063	5,305
Institutional Investors [Member]
Segment Reporting Information [Line Items]
Capital Expenditures	777	647	1,921	2,514
Depreciation	222	252	674	765
Amortization	326	302	937	906
Investment Managers [Member]
Segment Reporting Information [Line Items]
Capital Expenditures	1,596	927	3,071	5,090
Depreciation	525	500	1,461	1,468
Amortization	218	201	626	603
Investments In New Businesses [Member]
Segment Reporting Information [Line Items]
Capital Expenditures	186	140	461	560
Depreciation	442	449	1,350	1,273
Amortization	419	332	1,204	905
Total From Business Segments [Member]
Segment Reporting Information [Line Items]
Capital Expenditures	15,448	12,759	41,012	46,177
Depreciation	5,509	5,615	16,711	16,338
Amortization	8,772	10,327	25,327	24,858
Corporate Overhead [Member]
Segment Reporting Information [Line Items]
Capital Expenditures	259	228	445	1,368
Depreciation	107	146	339	485
Amortization	$ 57	$ 57	$ 171	$ 555

Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Income Tax Contingency [Line Items]
Gross liability for unrecognized tax benefits, exclusive of interest and penalties	$ 12,731		$ 12,731		$ 11,553
Unrecognized tax benefits that would affect effective tax rate	10,608		10,608		9,965
Interest and penalties on unrecognized benefits	$ 957		$ 957		$ 770
Effective tax rates	28.50%	39.00%	33.30%	37.60%
Unrecognized tax benefits within the next twelve months	$ 4,985		$ 4,985

Income Taxes (Interest And Penalties) (Details) - USD ($) $ in Thousands	Sep. 30, 2013	Dec. 31, 2012
Income Tax Contingency [Line Items]
Gross liability for unrecognized tax benefits, exclusive of interest and penalties	$ 12,731	$ 11,553
Interest and penalties on unrecognized benefits	957	770
Gross uncertain tax positions	13,688	12,323
Amount included in Current liabilities	4,985	5,291
Amount included in Other long-term liabilities	$ 8,703	$ 7,032

Sale of SEI Asset Korea (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2013	Mar. 28, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of subsidiary (Note 13)	$ 0		$ 0	$ 22,112	$ 0
Gain on sale of subsidiary, diluted earnings per share Impact, net				$ 0.08
Assets	1,391,699			$ 1,391,699		$ 1,309,824
Cash and cash equivalents	527,214		397,677	527,214	397,677	452,247	$ 420,986
Net income	67,195		51,086	222,959	151,060
Less: Income attributable to the noncontrolling interests	0		(343)	$ (350)	(797)
SEI Asset Korea Co., Ltd. [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Closing date, sale of subsidiary				Mar. 28, 2013
Contingent purchase price from sale of SEI AK	11,220			$ 11,220
Expected proceeds by Company from purchase price from sale of SEI AK	$ 56,879			56,879
Sale of subsidiary transaction costs				2,545
Proceeds received at closing, net of transaction costs				$ 54,334
Percentage of ownership before sale of subsidiary		56.10%
Assets						54,783
Cash and cash equivalents						$ 48,306
Business segment that includes operating results of SEI AK		Private Banks
Revenues		$ 2,889	2,779		8,632
Net income		796	729		1,817
Less: Income attributable to the noncontrolling interests		(350)	(343)		(797)
Net income attributable to SEI AK		$ 446	$ 386		$ 1,020

Settlement Agreement (Details) - USD ($) $ in Thousands		3 Months Ended
Settlement Agreement (Details) - USD ($) $ in Thousands	Apr. 24, 2013	Sep. 30, 2013
Litigation Settlement [Abstract]
Settlement agreement date	Apr. 24, 2013
Cash settlement payment		$ 43,429