Capitalized software development costs in progress associated with future releases.

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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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Amount of expense for amortization of capitalized computer software costs.

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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.

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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.

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Amount of financial support provided to a nonconsolidated legal entity that is required to comply with or operate in accordance with requirements that are similar to those included in Rule 2a-7 of the Investment Company Act of 1940 for registered money market funds.

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Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as current. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, 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.

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Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Summary of Significant Accounting Policies [Line Items]
Cash and cash equivalents invested in SEI-sponsored money market funds	$ 793,883		$ 793,883		$ 784,626
Restricted cash	351		351		3,101
Capitalized software development costs			19,486	$ 18,640
Net book value of capitalized software	$ 250,280		$ 250,280		270,977
Anti-dilutive employee stock options (in shares)	11,347	8,813	11,531	8,342
Anti-dilutive employee stock options (in USD per share)	$ 57.80	$ 57.98	$ 57.78	$ 58.18
SEI Wealth Platform
Summary of Significant Accounting Policies [Line Items]
Capitalized software development costs			$ 19,387	$ 17,208
Net book value of capitalized software	$ 241,262		241,262
Capitalized software in progress	22,702		22,702		13,409
Amortization expense of capitalized software			$ 35,834	32,576
SEI Wealth Platform \| Weighted Average
Summary of Significant Accounting Policies [Line Items]
Weighted average remaining life (in years)			10 years
SEI-Sponsored Open-Ended Money Market Mutual Funds
Summary of Significant Accounting Policies [Line Items]
Cash and cash equivalents invested in SEI-sponsored money market funds	332,657		$ 332,657		347,082
SEI Investments (Europe) Limited
Summary of Significant Accounting Policies [Line Items]
Restricted cash	250		250		3,000
SEI Investments Distribution Co. (SIDCO)
Summary of Significant Accounting Policies [Line Items]
Restricted cash	101		101		$ 101
SEI-Sponsored Open-Ended Money Market Mutual Funds
Summary of Significant Accounting Policies [Line Items]
Fees waived	$ 11,629	$ 8,575	$ 33,118	$ 24,930