Investments - Amounts of Gross Realized Capital Gains and Gross Realized Capital Losses of Available For Sale Securities (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Gross realized capital gains	$ 15,600	$ 21,300	$ 26,900	$ 42,300
Gross realized capital losses	(4,500)	(8,400)	(25,700)	(16,400)
Net realized capital gains	$ 11,167	$ 12,942	$ 1,164	$ 25,873