Goodwill and Acquired Intangible Assets - Schedule of Goodwill (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Schedule of Goodwill [Roll Forward]
Balance as of January 1, 2018	$ 1,498,688
Measurement period adjustments	(1,986)
Foreign currency translation	(2,391)
Balance as of June 30, 2018	$ 1,494,311