Cash, Cash Equivalents and Restricted Cash - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents	$ 412,725	$ 390,263
Restricted cash and cash equivalents	6,074	17,929
Total cash, cash equivalents and restricted cash shown in the Consolidated Statements of Cash Flows	$ 418,799	$ 408,192	$ 641,759	$ 612,333