Segment and Geographic Information - Summary of Revenue and Long-lived Assets (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 75,491	$ 64,964	$ 152,262	$ 128,362
Long-lived assets	31,290		31,290		$ 32,185
United States [Member]
Segment Reporting Information [Line Items]
Revenues	65,937	55,045	132,390	108,621
Long-lived assets	21,848		21,848		23,099
United Kingdom [Member]
Segment Reporting Information [Line Items]
Revenues	9,200	9,701	19,264	19,359
Long-lived assets	9,418		9,418		9,057
Other [Member]
Segment Reporting Information [Line Items]
Revenues	354	$ 218	608	$ 382
Long-lived assets	$ 24		$ 24		$ 29