Investments - Schedule of Available For Sale Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Amortized Cost
Amortized Cost	$ 6,153,624	$ 6,231,018
Fair Value
Fair Value	5,882,359	5,876,721
U.S. Treasury securities:
Amortized Cost
Due in 1 year	245,299
Due after 1 but within 5 years	273,066
Due after 5 but within 10 years	21,754
Due after 10 years	14,478
Subtotal	554,597
Amortized Cost	554,597	561,853
Fair Value
Due in 1 year	244,122
Due after 1 but within 5 years	268,123
Due after 5 but within 10 years	20,207
Due after 10 years	12,810
Subtotal	545,262
Fair Value	545,262	547,290
Municipal debt securities
Amortized Cost
Due in 1 year	31,146
Due after 1 but within 5 years	169,668
Due after 5 but within 10 years	302,786
Due after 10 years	130,561
Subtotal	634,161
Amortized Cost	634,161	631,015
Fair Value
Due in 1 year	31,022
Due after 1 but within 5 years	163,972
Due after 5 but within 10 years	281,001
Due after 10 years	116,566
Subtotal	592,561
Fair Value	592,561	583,501
Non-U.S. government securities:
Amortized Cost
Due in 1 year	460
Due after 1 but within 5 years	32,019
Due after 5 but within 10 years	16,581
Due after 10 years	23,278
Subtotal	72,338
Amortized Cost	72,338	81,631
Fair Value
Due in 1 year	455
Due after 1 but within 5 years	31,168
Due after 5 but within 10 years	13,348
Due after 10 years	16,899
Subtotal	61,870
Fair Value	61,870	69,798
Corporate debt securities:
Amortized Cost
Due in 1 year	207,925
Due after 1 but within 5 years	630,168
Due after 5 but within 10 years	999,926
Due after 10 years	107,139
Subtotal	1,945,158
Amortized Cost	1,945,158	1,887,647
Fair Value
Due in 1 year	206,923
Due after 1 but within 5 years	608,427
Due after 5 but within 10 years	968,511
Due after 10 years	83,630
Subtotal	1,867,491
Fair Value	1,867,491	1,783,046
U.S. agency mortgage-backed securities
Amortized Cost
Amortized Cost	1,254,479	1,249,259
Fair Value
Fair Value	1,165,643	1,125,436
Residential and commercial mortgage securities
Amortized Cost
Amortized Cost	505,931	519,613
Fair Value
Fair Value	470,481	478,086
Asset-backed securities
Amortized Cost
Amortized Cost	754,428	642,395
Fair Value
Fair Value	746,519	631,959
Money market funds
Amortized Cost
Amortized Cost	432,532	657,605
Fair Value
Fair Value	$ 432,532	$ 657,605

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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-Name Accounting Standards Codification
-Section 50
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479130/326-30-45-1

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