Investments - Schedule of Available For Sale Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Amortized Cost
Amortized Cost	$ 5,586,730	$ 5,184,856
Fair Value
Fair Value	5,263,739	4,741,625
U.S. Treasury securities
Amortized Cost
Due in 1 year	646,598
Due after 1 but within 5 years	313,901
Due after 5 but within 10 years	39,156
Due after 10 years	14,421
Subtotal	1,014,076
Amortized Cost	1,014,076	584,173
Fair Value
Due in 1 year	645,280
Due after 1 but within 5 years	301,424
Due after 5 but within 10 years	36,194
Due after 10 years	13,484
Subtotal	996,382
Fair Value	996,382	556,438
U.S. agency securities
Amortized Cost
Due in 1 year	7,199
Due after 1 but within 5 years	0
Subtotal	7,199
Amortized Cost	7,199	49,059
Fair Value
Due in 1 year	7,195
Due after 1 but within 5 years	0
Subtotal	7,195
Fair Value	7,195	49,058
Municipal debt securities
Amortized Cost
Due in 1 year	2,139
Due after 1 but within 5 years	82,614
Due after 5 but within 10 years	138,354
Due after 10 years	361,940
Subtotal	585,047
Amortized Cost	585,047	661,934
Fair Value
Due in 1 year	2,121
Due after 1 but within 5 years	80,349
Due after 5 but within 10 years	130,186
Due after 10 years	334,602
Subtotal	547,258
Fair Value	547,258	602,690
Non-U.S. government securities
Amortized Cost
Due in 1 year	0
Due after 1 but within 5 years	36,715
Due after 5 but within 10 years	5,530
Due after 10 years	35,271
Subtotal	77,516
Amortized Cost	77,516	69,651
Fair Value
Due in 1 year	0
Due after 1 but within 5 years	35,362
Due after 5 but within 10 years	4,520
Due after 10 years	27,565
Subtotal	67,447
Fair Value	67,447	62,399
Corporate debt securities
Amortized Cost
Due in 1 year	176,918
Due after 1 but within 5 years	472,817
Due after 5 but within 10 years	581,238
Due after 10 years	149,560
Subtotal	1,380,533
Amortized Cost	1,380,533	1,546,513
Fair Value
Due in 1 year	175,145
Due after 1 but within 5 years	453,496
Due after 5 but within 10 years	543,115
Due after 10 years	125,299
Subtotal	1,297,055
Fair Value	1,297,055	1,414,321
U.S. agency mortgage-backed securities
Amortized Cost
Amortized Cost	922,907	898,675
Fair Value
Fair Value	821,346	783,743
Residential and commercial mortgage securities
Amortized Cost
Amortized Cost	571,163	577,915
Fair Value
Fair Value	517,940	511,824
Asset-backed securities
Amortized Cost
Amortized Cost	584,168	660,345
Fair Value
Fair Value	564,995	624,561
Money market funds
Amortized Cost
Amortized Cost	444,121	136,591
Fair Value
Fair Value	$ 444,121	$ 136,591

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
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-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
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