Segment and Geographical Information - Revenues based on Geographical Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues, net	$ 183,033	$ 167,036
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues, net	150,281	134,074
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues, net	26,082	27,428
Rest of World
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues, net	6,670	5,534
Non-US
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues, net	$ 32,752	$ 32,962