Property and Equipment - Net - Schedule of Long Lived Tangible Assets by Geographic Area (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Revenues From External Customers And Long Lived Assets [Line Items]
Total long-lived tangible assets	$ 17,688	$ 18,707
United States [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Total long-lived tangible assets	17,214	18,217
International [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Total long-lived tangible assets	$ 474	$ 490