Acquisitions, Intangible Assets and Goodwill - Additional Information (Details) - USD ($) $ in Thousands			1 Months Ended				12 Months Ended
	Jul. 31, 2015	May 20, 2015	Nov. 30, 2016	Aug. 31, 2016	Jul. 31, 2015	May 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Aug. 31, 2016	Dec. 31, 2015
Acquisitions Intangible Assets And Goodwill [Line Items]
Residual of goodwill							$ 336,861	$ 336,861	$ 336,861		$ 349,043
Intangibles derecognized, carrying value									3,700
Amortization expense related to capitalized internal-use software							21,700	21,100	19,400
Amortization expense							4,270	4,461	$ 8,772
Capitalized internal-use software, net							33,280	$ 41,493
Capitalized Internal-Use Software Net in Development Phase
Acquisitions Intangible Assets And Goodwill [Line Items]
Capitalized internal-use software, net							$ 13,600
Renzu
Acquisitions Intangible Assets And Goodwill [Line Items]
Closing date of acquisition		May 20, 2015
Total purchase price						$ 17,000
Issuance of common stock						10,300
Cash payment						6,700
Business combination, net tangible liabilities						700
Business combination, fair value identifiable intangible assets						5,500
Residual of goodwill						$ 12,200
Goodwill derecognized, carrying value			$ 12,200
Intangibles derecognized, carrying value			$ 3,700
TechValidate
Acquisitions Intangible Assets And Goodwill [Line Items]
Closing date of acquisition	Jul. 31, 2015
Total purchase price					$ 60,400
Issuance of common stock					23,800
Cash payment	$ 22,200			$ 14,400						$ 36,600
Business combination, net tangible liabilities	5,800				5,800
Business combination, fair value identifiable intangible assets	15,800				15,800
Residual of goodwill	$ 50,400				$ 50,400