Operating Segment and Enterprise Wide Reporting - Schedule of Net Long-lived Tangible Assets by Location (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Revenues From External Customers And Long Lived Assets [Line Items]
Net long-lived tangible assets	$ 23,894	$ 27,569
United States [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Net long-lived tangible assets	22,150	24,914
United Kingdom [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Net long-lived tangible assets	782	1,176
Europe (Excluding United Kingdom) [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Net long-lived tangible assets	259	381
Other [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Net long-lived tangible assets	$ 703	$ 1,098