Equity Method Investments and Other - Net Investment Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Schedule of Equity Method Investments [Line Items]
Net investment income	$ 80,686	$ 40,322	$ 36,931
Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Net investment income	2,524	(9,434)	6,015
Dowling Capital Partners LP units \| Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Net investment income	1,463	927	502
RISCOM \| Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Net investment income	1,492	884	1,471
Brewer Lane Ventures Fund II LP \| Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Net investment income	(110)	(78)	0
Hudson Ventures Fund II LP units \| Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Net investment income	(153)	170	379
JVM Funds LLC \| Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Net investment income	(1,554)	(1,198)	(70)
Universa Black Swan LP units \| Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Net investment income	0	(988)	(3,028)
Arena SOP LP units \| Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Net investment income	(989)	(6,271)	3,042
Arena Special Opportunities Fund, LP units \| Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Net investment income	$ 2,375	$ (2,880)	$ 3,719