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Investments Investments (Available for Sale) (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Total fixed maturities, Amortized Cost	$ 3,991,871		$ 3,663,031
Gross Unrealized Holding Gains	33,391		11,601
Gross Unrealized Holding Losses	107,142		137,042
Allowance for Credit Losses	(42)	$ (47)	(27)	$ (67)	$ (543)	$ (553)
Estimated Fair Value	3,918,078		3,537,563
U.S. Treasury securities and obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Total fixed maturities, Amortized Cost	7,839		15,465
Gross Unrealized Holding Gains	12		0
Gross Unrealized Holding Losses	241		417
Allowance for Credit Losses	0		0
Estimated Fair Value	7,610		15,048
Obligations of states, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Total fixed maturities, Amortized Cost	158,963		168,894
Gross Unrealized Holding Gains	190		46
Gross Unrealized Holding Losses	21,570		22,633
Allowance for Credit Losses	(3)		(3)
Estimated Fair Value	137,580		146,304
Corporate and other securities
Debt Securities, Available-for-sale [Line Items]
Total fixed maturities, Amortized Cost	2,114,850		2,037,372
Gross Unrealized Holding Gains	21,041		5,779
Gross Unrealized Holding Losses	35,818		53,638
Allowance for Credit Losses	(39)		(23)
Estimated Fair Value	2,100,034		1,989,490
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Total fixed maturities, Amortized Cost	777,402		729,658
Gross Unrealized Holding Gains	7,113		4,606
Gross Unrealized Holding Losses	608		1,522
Allowance for Credit Losses	0		0
Estimated Fair Value	783,907		732,742
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Total fixed maturities, Amortized Cost	607,220		502,121
Gross Unrealized Holding Gains	2,461		747
Gross Unrealized Holding Losses	45,890		53,994
Allowance for Credit Losses	0		0
Estimated Fair Value	563,791		448,874
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Total fixed maturities, Amortized Cost	325,597		209,521
Gross Unrealized Holding Gains	2,574		423
Gross Unrealized Holding Losses	3,015		4,838
Allowance for Credit Losses	0		(1)
Estimated Fair Value	$ 325,156		$ 205,105