Goodwill and Acquired Intangible Assets - Schedule of Acquired Intangible Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 399,191	$ 402,801
Accumulated Amortization	(222,551)	(201,542)
Net Carrying Amount	176,640	201,259
Completed technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	145,091	145,091
Accumulated Amortization	(77,512)	(65,283)
Net Carrying Amount	67,579	79,808
Customer-related intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	245,710	245,310
Accumulated Amortization	(140,798)	(128,835)
Net Carrying Amount	104,912	116,475
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	700	4,710
Accumulated Amortization	(256)	(3,975)
Net Carrying Amount	444	735
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	7,200	7,200
Accumulated Amortization	(3,495)	(2,959)
Net Carrying Amount	3,705	4,241
Acquired license rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	490	490
Accumulated Amortization	(490)	(490)
Net Carrying Amount	$ 0	$ 0