Investments - Schedule of Available For Sale Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Amortized Cost
Amortized Cost	$ 6,167,937	$ 5,586,730
Fair Value
Fair Value	5,950,499	5,263,739
U.S. Treasury securities
Amortized Cost
Due in 1 year	374,834
Due after 1 but within 5 years	296,218
Due after 5 but within 10 years	32,419
Due after 10 years	14,455
Subtotal	717,926
Amortized Cost	717,926	1,014,076
Fair Value
Due in 1 year	374,240
Due after 1 but within 5 years	291,269
Due after 5 but within 10 years	30,787
Due after 10 years	13,511
Subtotal	709,807
Fair Value	709,807	996,382
Municipal debt securities
Amortized Cost
Due in 1 year	11,311
Due after 1 but within 5 years	85,784
Due after 5 but within 10 years	133,431
Due after 10 years	374,600
Subtotal	605,126
Amortized Cost	605,126	585,047
Fair Value
Due in 1 year	11,178
Due after 1 but within 5 years	84,460
Due after 5 but within 10 years	128,002
Due after 10 years	354,007
Subtotal	577,647
Fair Value	577,647	547,258
Non-U.S. government securities:
Amortized Cost
Due in 1 year	5,263
Due after 1 but within 5 years	32,045
Due after 5 but within 10 years	7,712
Due after 10 years	36,688
Subtotal	81,708
Amortized Cost	81,708	77,516
Fair Value
Due in 1 year	5,211
Due after 1 but within 5 years	31,271
Due after 5 but within 10 years	6,649
Due after 10 years	29,840
Subtotal	72,971
Fair Value	72,971	67,447
Corporate debt securities:
Amortized Cost
Due in 1 year	165,056
Due after 1 but within 5 years	480,233
Due after 5 but within 10 years	897,438
Due after 10 years	210,171
Subtotal	1,752,898
Amortized Cost	1,752,898	1,380,533
Fair Value
Due in 1 year	164,117
Due after 1 but within 5 years	469,192
Due after 5 but within 10 years	880,803
Due after 10 years	190,276
Subtotal	1,704,388
Fair Value	1,704,388	1,297,055
U.S. agency mortgage-backed securities
Amortized Cost
Amortized Cost	1,131,788	922,907
Fair Value
Fair Value	1,051,308	821,346
Residential and commercial mortgage securities
Amortized Cost
Amortized Cost	539,283	571,163
Fair Value
Fair Value	503,980	517,940
Asset-backed securities
Amortized Cost
Amortized Cost	556,886	584,168
Fair Value
Fair Value	548,076	564,995
Money market funds
Amortized Cost
Amortized Cost	782,322	444,121
Fair Value
Fair Value	$ 782,322	$ 444,121

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
-Subparagraph (SX 210.7-03(a)(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
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-Section 45
-Paragraph 1
-Publisher FASB
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