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Investments and Other Marketable Securities - Available-for-Sale and Equity Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, Cost Amount	$ 162,657	$ 154,211
Available for sale debt securities, Fair Value	156,374	143,126
Available for sale and equity securities, Cost Amount	212,665	192,794
Available for sale and equity securities, Gross Unrealized Gains	2,666	1,947
Available for sale and equity securities, Gross Unrealized (Losses)	(6,283)	(11,085)
Available for sale and equity securities, Fair Value	209,048	183,656
Available-for-sale debt securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, Cost Amount	162,657	154,211
Available-for-sale debt securities, Gross Unrealized Gains	0	0
Available-for-sale debt securities, Gross Unrealized (Losses)	(6,283)	(11,085)
Available for sale debt securities, Fair Value	156,374	143,126
SEI-sponsored investment products
Debt Securities, Available-for-sale [Line Items]
Equity securities, FV-NI, Cost Amount	44,162	33,029
Equity securities, FV-NI, Gross Unrealized Gains	2,155	1,615
Equity securities, FV-NI, Gross Unrealized (Losses)	0	0
Equity securities, FV-NI, Fair Value	46,317	34,644
Equities and other investment products
Debt Securities, Available-for-sale [Line Items]
Equity securities, FV-NI, Cost Amount	5,846	5,554
Equity securities, FV-NI, Gross Unrealized Gains	511	332
Equity securities, FV-NI, Gross Unrealized (Losses)	0	0
Equity securities, FV-NI, Fair Value	$ 6,357	$ 5,886

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