Investments - Schedule of Available for Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 6,231,018	$ 5,586,730
Unrealized Gains	4,155	13,446
Unrealized Losses	(358,452)	(336,437)
Fair Value	5,876,721	5,263,739
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	561,853	1,014,076
Unrealized Gains	325	1,434
Unrealized Losses	(14,888)	(19,128)
Fair Value	547,290	996,382
U.S. agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		7,199
Unrealized Gains		0
Unrealized Losses		(4)
Fair Value		7,195
U.S. agency mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,249,259	922,907
Unrealized Gains	42	438
Unrealized Losses	(123,865)	(101,999)
Fair Value	1,125,436	821,346
Municipal debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	631,015	585,047
Unrealized Gains	1,596	6,660
Unrealized Losses	(49,110)	(44,449)
Fair Value	583,501	547,258
Non-U.S. government securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	81,631	77,516
Unrealized Gains	0	0
Unrealized Losses	(11,833)	(10,069)
Fair Value	69,798	67,447
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,887,647	1,380,533
Unrealized Gains	1,064	4,425
Unrealized Losses	(105,665)	(87,903)
Fair Value	1,783,046	1,297,055
Residential and commercial mortgage securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	519,613	571,163
Unrealized Gains	527	286
Unrealized Losses	(42,054)	(53,509)
Fair Value	478,086	517,940
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	642,395	584,168
Unrealized Gains	601	203
Unrealized Losses	(11,037)	(19,376)
Fair Value	631,959	564,995
Money market funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	657,605	444,121
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	$ 657,605	$ 444,121

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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