Segment and Geographic Information - Summary of Revenue and Long-lived Assets (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 76,771	$ 63,398
Long-lived assets	31,190		32,185
United States [Member]
Segment Reporting Information [Line Items]
Revenues	66,453	53,576
Long-lived assets	22,265		23,099
United Kingdom [Member]
Segment Reporting Information [Line Items]
Revenues	10,065	9,658
Long-lived assets	8,902		9,057
Other [Member]
Segment Reporting Information [Line Items]
Revenues	253	164
Long-lived assets	$ 23		$ 29