Summary of Cash, Cash Equivalents and Restricted Cash Reported In Consolidated Statements of Cash Flows (Detail) - USD ($) $ in Thousands		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash And Cash Equivalents Period Increase Decrease [Abstract]
Cash and cash equivalents		$ 1,224,490	$ 61,268	$ 105,220
Restricted cash	[1]	$ 54,664	$ 44,399	$ 94,465
Restricted Cash and Cash Equivalents, Noncurrent, Asset, Statement of Financial Position [Extensible List]		us-gaap:OtherAssetsMember	us-gaap:OtherAssetsMember	us-gaap:OtherAssetsMember
Total cash, cash equivalents and restricted cash		$ 1,279,154	$ 105,667	$ 199,685

[1] (a)Restricted cash is included in other assets on the accompanying consolidated balance sheet and consists of statutorily required capital reserves related to our commercial insurance subsidiary.