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Investments Investments (Available for Sale) (Details) - USD ($) $ in Thousands	Sep. 30, 2026	Jun. 30, 2026	Dec. 31, 2025	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Total fixed maturities, Amortized Cost	$ 4,736,687		$ 4,382,725
Gross Unrealized Holding Gains	715		45,250
Gross Unrealized Holding Losses	240,022		86,496
Allowance for Credit Losses	(55)	$ (56)	(29)	$ (38)	$ (42)	$ (27)
Estimated Fair Value	4,497,325		4,341,450
U.S. Treasury securities and obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Total fixed maturities, Amortized Cost	869		861
Gross Unrealized Holding Gains	0		14
Gross Unrealized Holding Losses	31		1
Allowance for Credit Losses	0		0
Estimated Fair Value	838		874
Obligations of states, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Total fixed maturities, Amortized Cost	101,347		146,222
Gross Unrealized Holding Gains	1		51
Gross Unrealized Holding Losses	22,594		18,410
Allowance for Credit Losses	(2)		(3)
Estimated Fair Value	78,752		127,860
Corporate and other securities
Debt Securities, Available-for-sale [Line Items]
Total fixed maturities, Amortized Cost	1,831,099		1,711,348
Gross Unrealized Holding Gains	59		28,798
Gross Unrealized Holding Losses	99,093		26,232
Allowance for Credit Losses	(53)		(26)
Estimated Fair Value	1,732,012		1,713,888
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Total fixed maturities, Amortized Cost	538,114		582,780
Gross Unrealized Holding Gains	464		6,377
Gross Unrealized Holding Losses	7,309		638
Allowance for Credit Losses	0		0
Estimated Fair Value	531,269		588,519
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Total fixed maturities, Amortized Cost	1,755,050		1,491,642
Gross Unrealized Holding Gains	103		6,378
Gross Unrealized Holding Losses	99,365		38,750
Allowance for Credit Losses	0		0
Estimated Fair Value	1,655,788		1,459,270
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Total fixed maturities, Amortized Cost	510,208		449,872
Gross Unrealized Holding Gains	88		3,632
Gross Unrealized Holding Losses	11,630		2,465
Allowance for Credit Losses	0		0
Estimated Fair Value	$ 498,666		$ 451,039