Segment Reporting - Revenues by Geographic Area, Based on Billing Location of Customer and Long-Lived Assets, by Geographical Areas (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues, net	$ 74,991	$ 99,878	$ 108,530
Total long-lived assets, net	15,559	20,581
United States of America [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues, net	49,637	69,220	72,942
Total long-lived assets, net	15,069	19,861
International [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues, net	25,354	30,658	$ 35,588
Total long-lived assets, net	$ 490	$ 720