Segment & Geographical Information Segment & Geographical Information - Revenues Based on Geographical Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues, net
Revenues, net	$ 177,274	$ 171,200	$ 170,478	$ 167,036	$ 165,858	$ 163,503	$ 155,621	$ 143,510	$ 685,988	$ 628,492	$ 499,278
Property, Plant and Equipment, net
Property, plant and equipment, net	49,029				47,991				49,029	47,991
United States
Revenues, net
Revenues, net									554,945	496,418	368,870
Property, Plant and Equipment, net
Property, plant and equipment, net	10,809				10,680				10,809	10,680
United Kingdom
Revenues, net
Revenues, net									109,905	108,868	101,789
Rest of World
Revenues, net
Revenues, net									21,138	23,206	28,619
Property, Plant and Equipment, net
Property, plant and equipment, net	2,958				2,611				2,958	2,611
Non-US
Revenues, net
Revenues, net									131,043	132,074	$ 130,408
India
Property, Plant and Equipment, net
Property, plant and equipment, net	23,362				23,415				23,362	23,415
Philippines
Property, Plant and Equipment, net
Property, plant and equipment, net	$ 11,900				$ 11,285				$ 11,900	$ 11,285