Components of Net Realized Investment Gains (Losses) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Total net realized investment gains (losses)	$ (32,929)	$ 15,887	$ (14,662)
Equity securities, Gross realized gains	2,289	15,350	16,997
Equity securities, Gross realized losses	(5,681)	(1,910)	(32,247)
Equity securities, Total net realized investment gains (losses)	(3,392)	13,440	(15,250)
Not Designated as Hedging Instrument | Interest Rate Swap
Schedule Of Available For Sale Securities [Line Items]
Gross realized gains	12,844	8,035	19,460
Gross realized losses	(2,771)	(5,930)	(41,716)
Total net realized investment gains (losses)	10,073	2,105	(22,256)
Fixed Income Securities
Schedule Of Available For Sale Securities [Line Items]
Gross realized gains	688	11,390	28,381
Gross realized losses	(40,298)	(11,048)	(5,537)
Total net realized investment gains (losses)	$ (39,610)	$ 342	$ 22,844