Cash, Cash Equivalents and Restricted Cash - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents	$ 416,352	$ 595,921
Restricted cash and cash equivalents	18,221	16,412
Total cash, cash equivalents, and restricted cash shown in the Consolidated Statements of Cash Flows	$ 434,573	$ 612,333	$ 600,088	$ 781,645