Investments and Other Marketable Securities - Available for Sale and Equity Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, Cost Amount	$ 171,780	$ 154,211
Available for sale debt securities, Fair Value	164,681	143,126
Available for sale and equity securities, Cost Amount	211,191	192,794
Available for sale and equity securities, Gross Unrealized Gains	2,122	1,947
Available for sale and equity securities, Gross Unrealized (Losses)	(7,099)	(11,085)
Available for sale and equity securities, Fair Value	206,214	183,656
Available-for-sale debt securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, Cost Amount	171,780	154,211
Available-for-sale debt securities, Gross Unrealized Gains	0	0
Available-for-sale debt securities, Gross Unrealized (Losses)	(7,099)	(11,085)
Available for sale debt securities, Fair Value	164,681	143,126
SEI-sponsored investment products
Debt Securities, Available-for-sale [Line Items]
Equity securities, FV-NI, Cost Amount	33,569	33,029
Equity securities, FV-NI, Gross Unrealized Gains	1,944	1,615
Equity securities, FV-NI, Gross Unrealized (Losses)	0	0
Equity securities, FV-NI, Fair Value	35,513	34,644
Equities and other investment products
Debt Securities, Available-for-sale [Line Items]
Equity securities, FV-NI, Cost Amount	5,842	5,554
Equity securities, FV-NI, Gross Unrealized Gains	178	332
Equity securities, FV-NI, Gross Unrealized (Losses)	0	0
Equity securities, FV-NI, Fair Value	$ 6,020	$ 5,886