Interim Consolidated Financial Statements - Summary of End-of-period Cash and Cash Equivalents and Cash, Cash Equivalents and Restricted Cash from Financial Statements (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents	$ 67,629	$ 140,296	$ 92,057
Restricted cash, current	$ 717
Restricted Cash, Current, Asset, Statement of Financial Position [Extensible List]	us-gaap:PrepaidExpenseAndOtherAssetsCurrent
Restricted cash, non-current	$ 628
Restricted Cash, Noncurrent, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent
Cash, cash equivalents and restricted cash shown in statement of cash flows	$ 68,974		$ 92,057