Investments - Schedule of Available for Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 5,184,856	$ 4,897,607
Unrealized Gains	4,273	98,747
Unrealized Losses	(447,504)	(33,467)
Fair Value	4,741,625	4,962,887
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	584,173	447,926
Unrealized Gains	341	3,833
Unrealized Losses	(28,076)	(2,966)
Fair Value	556,438	448,793
U.S. agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	49,059	5,501
Unrealized Gains	7	3
Unrealized Losses	(8)	0
Fair Value	49,058	5,504
U.S. agency mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	898,675	1,005,611
Unrealized Gains	258	13,365
Unrealized Losses	(115,190)	(10,113)
Fair Value	783,743	1,008,863
Municipal debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	661,934	598,764
Unrealized Gains	2,010	30,122
Unrealized Losses	(61,254)	(1,287)
Fair Value	602,690	627,599
Non-U.S. government securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	69,651	77,366
Unrealized Gains	0	3,232
Unrealized Losses	(7,252)	(855)
Fair Value	62,399	79,743
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,546,513	1,428,645
Unrealized Gains	1,195	36,067
Unrealized Losses	(133,387)	(9,465)
Fair Value	1,414,321	1,455,247
Residential and commercial mortgage securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	577,915	541,638
Unrealized Gains	390	10,452
Unrealized Losses	(66,481)	(6,667)
Fair Value	511,824	545,423
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	660,345	582,144
Unrealized Gains	72	1,673
Unrealized Losses	(35,856)	(2,114)
Fair Value	624,561	581,703
Money market funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	136,591	210,012
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	$ 136,591	$ 210,012

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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-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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Amount, before tax, of unrealized loss 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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