Summary of Significant Accounting Policies (Policy)	3 Months Ended
Summary of Significant Accounting Policies (Policy)	Mar. 31, 2016
Accounting Policies [Abstract]
Basis of Presentation	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 have 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 March 31, 2016, the results of operations for the three months ended March 31, 2016 and 2015, and cash flows for the three month periods ended March 31, 2016 and 2015. 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, 2015. There have been no significant changes in significant accounting policies during the three months ended March 31, 2016 as compared to the significant accounting policies described in the Company’s Annual Report on Form 10-K for the year ended December 31, 2015 with the exception of the adoption of Accounting Standards Update (ASU) No. 2015-02, Consolidation (Topic 810) - Amendments to the Consolidation Analysis (See Note 3) and ASU No. 2015-07, Fair Value Measurement (Topic 820) - Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (See Note 5).
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.
New Accounting Pronouncements	New Accounting Pronouncements On May 28, 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (ASU 2014-09), requiring an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. ASU 2014-09 also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. The updated standard permits the use of either the retrospective or cumulative effect transition method. ASU 2014-09 currently becomes effective for the Company during the first quarter 2018. The Company is currently evaluating the transition method that will be elected and the effect that the updated standard will have on its consolidated financial statements and related disclosures. In March 2016, the FASB issued ASU No. 2016-08, Principal versus Agent Considerations (Reporting Revenue Gross versus Net) (ASU 2016-08), that amends the principal versus agent guidance in ASU 2014-09. ASU 2016-08 clarifies that the analysis must focus on whether the entity has control of the goods or services before they are transferred to the customer. ASU 2016-08 also provides additional guidance about how to apply the control principle when services are provided and when goods or services are combined with other goods or services. The effective date of the standard for the Company will coincide with ASU 2014-09 during the first quarter 2018. The Company is currently evaluating the effect that the updated standard will have on its consolidated financial statements and related disclosures. In April 2016, the FASB issued ASU No. 2016-10, Identifying Performance Obligations and Licensing (ASU 2016-10) that amends the revenue guidance in ASU 2014-09 on identifying performance obligations and accounting for licenses of intellectual property. ASU 2016-10 changed the FASB's previous proposals on renewals of right-to-use licenses and contractual restrictions. The effective date of the standard for the Company will coincide with ASU 2014-09 during the first quarter 2018. The Company is currently evaluating the effect that the updated standard will have on its consolidated financial statements and related disclosures. In January 2016, the FASB issued ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities (ASU 2016-01) that will significantly change the income statement impact of equity investments held by an entity, and the recognition of changes in fair value of financial liabilities when the fair value option is elected. ASU 2016-01 becomes effective for the Company during the first quarter 2018. The Company is currently evaluating the effect that the updated standard will have on its consolidated financial statements and related disclosures. In February 2016, the FASB issued ASU No. 2016-02, Leases (ASU 2016-02) requiring lessees to recognize a right-of-use asset and a lease liability on the balance sheet for all leases with the exception of short-term leases. For lessees, leases will continue to be classified as either operating or finance leases in the income statement. Lessor accounting is similar to the current model but updated to align with certain changes to the lessee model. Lessors will continue to classify leases as operating, direct financing or sales-type leases. The new standard must be adopted using a modified retrospective transition and requires application of the new guidance at the beginning of the earliest comparative period presented. The updated standard is effective for the Company beginning in the first quarter of 2019. Early adoption is permitted. The Company is currently evaluating the transition method that will be elected and the effect that the updated standard will have on its consolidated financial statements and related disclosures. In March 2016, the FASB issued ASU No. 2016-09, Improvements to Employee Share-Based Payment Accounting (ASU 2016-09) requiring an entity to record all excess tax benefits and tax deficiencies as an income tax benefit or expense in the income statement. ASU 2016-09 will also require an entity to elect an accounting policy to either estimate the number of forfeitures or account for forfeitures when they occur. ASU 2016-09 becomes effective for the Company during the first quarter 2017. The Company is currently evaluating the effect that the updated standard will have on its consolidated financial statements and related disclosures.
Reclassifications	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 has adopted the amendments contained in ASU No. 2015-02, Consolidation (Topic 810) - Amendments to the Consolidation Analysis (ASU 2015-02) during the first quarter 2016. ASU 2015-02 amends the current guidance for both the VIE and the voting interest entity (VOE) consolidation models. This guidance rescinds the indefinite deferral of the VIE guidance for investment companies that permitted application of the risks and rewards based approach. The Company has concluded that it is not the primary beneficiary of the entities and; therefore, is not required to consolidate any of the pooled investment vehicles for which it receives asset management, distribution, administration and custodial fees under the VIE model. The entities either do not meet the definition of a VIE or the Company does not hold a variable interest in the entities. The entities either qualify for the money market scope exception, or are entities in which the Company’s asset management, distribution, administration and custodial fees are commensurate with the services provided and include fair terms and conditions, or are entities that are limited partnerships which have substantive kick-out rights. The Company acts as a fiduciary and does not hold any other interests other than insignificant seed money investments in the pooled investment vehicles. For this reason, the Company also concluded that it is not required to consolidate the pooled investment vehicles under the VOE model.
Fair Value of Financial Instruments	The fair value of the Company’s financial assets and liabilities, except for the Company's investment funds sponsored by LSV, 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 open-ended mutual funds that are quoted daily. Level 2 financial assets consist of Government National Mortgage Association (GNMA) mortgage-backed securities held by the Company's wholly-owned limited purpose federal thrift subsidiary, SEI Private Trust Company (SPTC), Federal Home Loan Bank (FHLB) and other U.S. government agency short-term notes and investment grade commercial paper held by SIDCO. The financial assets held by SIDCO were purchased as part of a cash management program requiring only short term, top-tier investment grade government and corporate securities. The financial assets held by SPTC are debt securities issued by GNMA and are backed by the full faith and credit of the U.S. government. These securities were purchased for the sole purpose of satisfying applicable regulatory requirements and have maturity dates which range from 2020 to 2041. The Company has retrospectively adopted ASU No. 2015-07, Fair Value Measurement (Topic 820) - Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (ASU 2015-07) during the first quarter 2016 for all periods presented. The fair value of the Company's investment funds sponsored by LSV is measured using the net asset value per share (NAV) as a practical expedient. The NAVs of the funds are calculated by the funds' independent custodian and are derived from the fair values of the underlying investments as of the reporting date. The funds allow for investor redemptions at the end of each calendar month. In accordance with ASU 2015-07, this investment has not been classified in the fair value hierarchy. The valuation of the Company's Level 2 financial assets held by SIDCO and SPTC are based upon securities pricing policies and procedures utilized by third-party pricing vendors. The pricing policies and procedures applied during the three months ended March 31, 2016 were consistent with those as described in our Annual Report on Form 10-K at December 31, 2015.
Available-for-sale Securities	These net unrealized gains and losses are reported as a separate component of Accumulated other comprehensive loss on the accompanying Consolidated Balance Sheets.
Investments in Affiliated Funds	The fair value of the Company's investment funds sponsored by LSV is measured using the net asset value per share (NAV) as a practical expedient. The NAVs of the funds are calculated by the funds' independent custodian and are derived from the fair values of the underlying investments as of the reporting date. The funds allow for investor redemptions at the end of each calendar month. In accordance with ASU 2015-07, this investment has not been classified in the fair value hierarchy.
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.