Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ / shares in Units, shares in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Summary of Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 839,891,000	$ 834,697,000
Restricted cash	302,000	301,000
Impairment charge on reclassified assets	0	0	$ 0
Capitalized software development costs	24,340,000	33,958,000	35,293,000
Net book value of capitalized software	236,023,000	239,783,000
Impairment charges related to capitalized software development costs	0	5,250,000	0
Goodwill and intangible assets impairment	$ 0	$ 0	$ 0
Anti-dilutive employee stock options (in shares)	9,530	11,388	12,439
Anti-dilutive employee stock options, average exercise price per share (in usd per share)	$ 61.83	$ 61.32	$ 60.35
Investment Managers
Summary of Significant Accounting Policies [Line Items]
Capitalized software development costs	$ 10,644,000	$ 15,775,000	$ 9,558,000
Capitalized software development costs in progress	30,812,000	20,083,000
SEI Wealth Platform
Summary of Significant Accounting Policies [Line Items]
Capitalized software development costs	13,696,000	18,183,000	25,735,000
Net book value of capitalized software	204,621,000
Capitalized software development costs in progress	4,300,000
Amortization expense related to the SEI Wealth Platform	$ 27,510,000	25,637,000	35,638,000
Weighted Average | SEI Wealth Platform
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of the SEI Wealth Platform	8 years 2 months 12 days
Buildings | Minimum
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment	25 years
Buildings | Maximum
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment	39 years
Building Improvements | Minimum
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment	5 years
Building Improvements | Maximum
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment	15 years
Computer Equipment | Minimum
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment	3 years
Computer Equipment | Maximum
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment	5 years
Purchased Software | Minimum
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment	3 years
Purchased Software | Maximum
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment	5 years
Furniture and fixtures | Minimum
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment	3 years
Furniture and fixtures | Maximum
Summary of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment	5 years
SEI Sponsored Open Ended Money Market Mutual Funds
Summary of Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 341,311,000	397,838,000
SEI Investments Europe Limited
Summary of Significant Accounting Policies [Line Items]
Restricted cash	250,000	250,000
SEI Investments Distribution Co
Summary of Significant Accounting Policies [Line Items]
Restricted cash	52,000	51,000
SEI Sponsored Open Ended Money Market Mutual Funds
Summary of Significant Accounting Policies [Line Items]
Fees waived according to expense limitation agreements	$ 7,538,000	$ 22,092,000	$ 35,426,000