Goodwill and Acquired Intangible Assets - Schedule of Other Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 402,801	$ 321,121
Accumulated amortization	(201,542)	(171,658)
Net carrying amount	201,259	149,463
Completed technologies
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	145,091	119,091
Accumulated amortization	(65,283)	(50,823)
Net carrying amount	79,808	68,268
Customer-related intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	245,310	192,810
Accumulated amortization	(128,835)	(114,209)
Net carrying amount	116,475	78,601
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,710	5,030
Accumulated amortization	(3,975)	(3,775)
Net carrying amount	735	1,255
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	7,200	3,700
Accumulated amortization	(2,959)	(2,361)
Net carrying amount	4,241	1,339
Acquired license rights
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	490	490
Accumulated amortization	(490)	(490)
Net carrying amount	$ 0	$ 0