Schedule of Amortized Cost and Estimated Fair Value of Company's Fixed Maturities Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities, Amortized Cost	$ 1,323,666	$ 1,394,639
Fixed maturities, Allowance for Expected Credit Losses	0	0
Fixed maturities, Gross Unrealized Gains	3,050	2,205
Fixed maturities, Gross Unrealized losses	(11,317)	(14,936)
Fixed maturities, Estimated Fair Value	1,315,399	1,381,908
U.S. Treasuries
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities, Amortized Cost	543,858	875,273
Fixed maturities, Allowance for Expected Credit Losses	0	0
Fixed maturities, Gross Unrealized Gains	74	757
Fixed maturities, Gross Unrealized losses	(422)	(784)
Fixed maturities, Estimated Fair Value	543,510	875,246
Obligations of States and Political Subdivisions
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities, Amortized Cost	17,099	17,125
Fixed maturities, Allowance for Expected Credit Losses	0	0
Fixed maturities, Gross Unrealized Gains	0	0
Fixed maturities, Gross Unrealized losses	(615)	(790)
Fixed maturities, Estimated Fair Value	16,484	16,335
Mortgage Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities, Amortized Cost	210,360	61,905
Fixed maturities, Allowance for Expected Credit Losses	0	0
Fixed maturities, Gross Unrealized Gains	862	299
Fixed maturities, Gross Unrealized losses	(2,586)	(3,284)
Fixed maturities, Estimated Fair Value	208,636	58,920
Asset-backed Securities
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities, Amortized Cost	143,084	137,445
Fixed maturities, Allowance for Expected Credit Losses	0	0
Fixed maturities, Gross Unrealized Gains	962	864
Fixed maturities, Gross Unrealized losses	(2,346)	(2,882)
Fixed maturities, Estimated Fair Value	141,700	135,427
Commercial Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities, Amortized Cost	69,010	68,041
Fixed maturities, Allowance for Expected Credit Losses	0	0
Fixed maturities, Gross Unrealized Gains	333	15
Fixed maturities, Gross Unrealized losses	(1,786)	(2,488)
Fixed maturities, Estimated Fair Value	67,557	65,568
Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities, Amortized Cost	247,440	158,798
Fixed maturities, Allowance for Expected Credit Losses	0	0
Fixed maturities, Gross Unrealized Gains	595	189
Fixed maturities, Gross Unrealized losses	(2,151)	(2,891)
Fixed maturities, Estimated Fair Value	245,884	156,096
Foreign Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities, Amortized Cost	92,815	76,052
Fixed maturities, Allowance for Expected Credit Losses	0	0
Fixed maturities, Gross Unrealized Gains	224	81
Fixed maturities, Gross Unrealized losses	(1,411)	(1,817)
Fixed maturities, Estimated Fair Value	$ 91,628	$ 74,316

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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