Supplemental Disclosures of Cash Flow Information - Summary of Noncash Transactions (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Stock-based compensation not involving cash	$ 44,843	$ 39,792	$ 37,034
Commitments for low-income housing interests	51,978	50,883	33,846
Exchanges of fixed maturity investments	243,156	193,449	84,312
Net unsettled security trades	$ 8,421	$ 39,851	$ 0