Restricted Cash - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents	$ 140,549	$ 142,655	$ 111,055	$ 105,831
Restricted cash included in other current assets		$ 8	$ 17	$ 46
Restricted Cash, Current, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsCurrent	us-gaap:OtherAssetsCurrent	us-gaap:OtherAssetsCurrent	us-gaap:OtherAssetsCurrent
Restricted cash included in other non-current assets	$ 1,612	$ 1,630	$ 1,572	$ 1,568
Restricted Cash, Noncurrent, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 142,161	$ 144,293	$ 112,644	$ 107,445