Investments - Schedule of Fair Values and Gross Unrealized Gains and Losses (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 3,016,032	$ 2,876,343
Gross Unrealized, Gains	22,992	5,820
Gross Unrealized, Losses	(109,907)	(158,622)
Fair Value	2,929,117	2,723,541
U.S. Treasury securities and obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	113,564	115,342
Gross Unrealized, Gains	2,645	1,207
Gross Unrealized, Losses	(221)	(489)
Fair Value	115,988	116,060
Municipal debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	669,223	684,523
Gross Unrealized, Gains	2,145	589
Gross Unrealized, Losses	(36,406)	(49,867)
Fair Value	634,962	635,245
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,073,047	1,949,800
Gross Unrealized, Gains	18,202	3,981
Gross Unrealized, Losses	(71,916)	(106,141)
Fair Value	2,019,333	1,847,640
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	39,905	44,104
Gross Unrealized, Gains	0	1
Gross Unrealized, Losses	(1,348)	(2,125)
Fair Value	38,557	41,980
Total bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,895,739	2,793,769
Gross Unrealized, Gains	22,992	5,778
Gross Unrealized, Losses	(109,891)	(158,622)
Fair Value	2,808,840	2,640,925
Short-term investments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	120,293	82,574
Gross Unrealized, Gains	0	42
Gross Unrealized, Losses	(16)	0
Fair Value	$ 120,277	$ 82,616

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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