Schedule of Amortized Cost and Estimated Fair Value of Company's Fixed Maturities Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities, Amortized Cost	$ 1,334,130	$ 1,301,723
Fixed maturities, Allowance for Expected Credit Losses	0	0
Fixed maturities, Gross Unrealized Gains	222	591
Fixed maturities, Gross Unrealized losses	(47,257)	(54,116)
Fixed maturities, Estimated Fair Value	1,287,095	1,248,198
U.S. Treasuries
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities, Amortized Cost	451,829	352,533
Fixed maturities, Allowance for Expected Credit Losses	0	0
Fixed maturities, Gross Unrealized Gains	13	0
Fixed maturities, Gross Unrealized losses	(6,671)	(8,430)
Fixed maturities, Estimated Fair Value	445,171	344,103
Obligations of States and Political Subdivisions
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities, Amortized Cost	27,975	33,471
Fixed maturities, Allowance for Expected Credit Losses	0	0
Fixed maturities, Gross Unrealized Gains	0	0
Fixed maturities, Gross Unrealized losses	(1,760)	(1,876)
Fixed maturities, Estimated Fair Value	26,215	31,595
Mortgage Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities, Amortized Cost	66,571	67,560
Fixed maturities, Allowance for Expected Credit Losses	0	0
Fixed maturities, Gross Unrealized Gains	18	165
Fixed maturities, Gross Unrealized losses	(7,487)	(5,609)
Fixed maturities, Estimated Fair Value	59,102	62,116
Asset-backed Securities
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities, Amortized Cost	208,011	198,161
Fixed maturities, Allowance for Expected Credit Losses	0	0
Fixed maturities, Gross Unrealized Gains	87	390
Fixed maturities, Gross Unrealized losses	(7,124)	(9,151)
Fixed maturities, Estimated Fair Value	200,974	189,400
Commercial Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities, Amortized Cost	85,375	104,777
Fixed maturities, Allowance for Expected Credit Losses	0	0
Fixed maturities, Gross Unrealized Gains	13	20
Fixed maturities, Gross Unrealized losses	(6,628)	(6,133)
Fixed maturities, Estimated Fair Value	78,760	98,664
Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities, Amortized Cost	331,758	353,622
Fixed maturities, Allowance for Expected Credit Losses	0	0
Fixed maturities, Gross Unrealized Gains	80	16
Fixed maturities, Gross Unrealized losses	(11,351)	(14,858)
Fixed maturities, Estimated Fair Value	320,487	338,780
Foreign Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities, Amortized Cost	162,611	191,599
Fixed maturities, Allowance for Expected Credit Losses	0	0
Fixed maturities, Gross Unrealized Gains	11	0
Fixed maturities, Gross Unrealized losses	(6,236)	(8,059)
Fixed maturities, Estimated Fair Value	$ 156,386	$ 183,540

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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