Basis of Presentation and Significant Accounting Policies - Schedule of 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 Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 116,328	$ 69,418	$ 157,383	$ 163,620
Restricted cash	2,825	2,475	2,475	2,375
Total cash, cash equivalents and restricted cash shown in the statement of cash flow	$ 119,153	$ 71,893	$ 159,858	$ 165,995