Segment Information - Revenue Classified by Major Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016		Jun. 30, 2017	Jun. 30, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 215,884	$ 212,074	[1]	$ 429,145	$ 427,030	[1]
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	204,052	202,821		407,715	406,290
United Kingdom Israel [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	10,904	8,440		19,364	19,032
CHINA
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 928	$ 813		$ 2,066	$ 1,708

[1] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmQwNTUxZjZiZmE3YzQzNmRhNDgyNjI4Njg2MGZlNTFkfFRleHRTZWxlY3Rpb246QkY3N0ZFNTY0NDI0QTJENUI1NEJFOTUxMzA2RkE2RDAM}