Summary of Significant Accounting Policies [Line Items]

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic net Income or Loss per outstanding limited partnership unit in the future and that were not included in the computation of diluted net income per limited partnership unit, because to do so would increase net income per unit amounts or decrease loss per unit amounts for the period presented.

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- Definition

Additions made to capitalized computer software costs during the period.

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- Definition

For each income statement presented, the amount charged to expense for amortization of capitalized computer software costs.

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- Definition

The carrying amount of capitalized computer software costs net of accumulated amortization as of the balance sheet date.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

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- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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Amount of gain (loss) on sale or disposal of intangible assets.

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The name of the income statement line item caption that includes the intangible asset impairment charge.

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The reportable segment in which the impaired intangible asset (excluding goodwill) resides.

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- Definition

The cash outflow associated with the acquisition from vendors of software programs or applications for internal use (that is, not to be sold, leased or otherwise marketed to others) that qualify for capitalization.

+ References

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The amount of a reclassification adjustment made to prior period financial statement amounts.

+ References

No definition available.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. For a classified balance sheet represents the current portion only (the noncurrent portion has a separate concept); there is a separate and distinct element for unclassified presentations.

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Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary of Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 679,661	$ 679,661	$ 667,446	$ 578,273	$ 452,247
Restricted cash	5,500	5,500	5,801
Capitalized software development costs		29,416	34,877	$ 39,500
Net book value of the SEI Wealth Platform	290,522	$ 290,522	309,040
Prior period reclassification adjustment			$ 1,414
Anti-dilutive employee stock options		10,730	10,166	7,736
Anti-dilutive employee stock options, average exercise price per share		$ 33.99	$ 30.00	$ 30.54
SEI Wealth Platform [Member]
Summary of Significant Accounting Policies [Line Items]
Capitalized software development costs		$ 24,515	$ 34,877	$ 39,500
Conversion option payment included in software development costs				8,812
Net book value of the SEI Wealth Platform	$ 285,621	285,621
Estimated useful life of the SEI Wealth Platform	15 years
Amortization expense related to the SEI Wealth Platform		$ 42,401	38,357	$ 34,045
Income statement classification for capitalized software write off related to the SEI Wealth Platform		Facilities, supplies and other costs
Sei Sponsored Open Ended Money Market Mutual Funds [Member]
Summary of Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 448,957	$ 448,957	435,268
Sei Investments Europe Limited [Member]
Summary of Significant Accounting Policies [Line Items]
Restricted cash	5,000	5,000	5,000
Sei Investments Distribution Co Sidco [Member]
Summary of Significant Accounting Policies [Line Items]
Restricted cash	$ 500	$ 500	$ 500
Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Equity method investment, ownership percentage	50.00%	50.00%
Weighted Average [Member] \| SEI Wealth Platform [Member]
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of the SEI Wealth Platform	6 years 6 months
Building and Building Improvements [Member] \| Minimum [Member]
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment		25 years
Building and Building Improvements [Member] \| Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment		39 years
Computer Equipment [Member] \| Minimum [Member]
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment		3 years
Computer Equipment [Member] \| Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment		5 years
Furniture and Fixtures [Member] \| Minimum [Member]
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment		3 years
Furniture and Fixtures [Member] \| Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment		5 years
Equity Method Investee [Member] \| Minimum [Member]
Summary of Significant Accounting Policies [Line Items]
Equity method investment, ownership percentage	20.00%	20.00%
Equity Method Investee [Member] \| Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Equity method investment, ownership percentage	50.00%	50.00%
Capitalized software [Member] \| SEI Wealth Platform [Member]
Summary of Significant Accounting Policies [Line Items]
Loss on write off of capitalized software related to the SEI Wealth Platform		$ 5,533
Private Banks [Member] \| SEI Wealth Platform [Member]
Summary of Significant Accounting Policies [Line Items]
Segment classification for capitalized software write off related to the SEI Wealth Platform		Private Banks
Investment Advisors [Member] \| SEI Wealth Platform [Member]
Summary of Significant Accounting Policies [Line Items]
Segment classification for capitalized software write off related to the SEI Wealth Platform		Investment Advisors