Summary of Cash, Cash Equivalents and Restricted Cash Reported In Consolidated Statements of Cash Flows (Detail) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash And Cash Equivalents Period Increase Decrease [Abstract]
Cash and cash equivalents		$ 105,220	$ 74,423	$ 33,747
Restricted cash	[1]	$ 94,465	$ 92,874	$ 88,203
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		$ 199,685	$ 167,297	$ 121,950

[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.