Summary of Cash and Cash Equivalents and Restricted Cash Balances (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 84,483	$ 53,380	$ 96,432
Restricted cash	152,962	157,914	141,610
Total cash and cash equivalents and restricted cash	$ 237,445	$ 211,294	$ 238,042	$ 300,710