Goodwill and Acquired Intangible Assets - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of acquired intangible assets	$ 8,294	$ 7,753	$ 25,019	$ 23,075
Future amortization expense to be recognized in remainder of 2018	8,300		8,300
Future amortization expense 2019	36,600		36,600
Future amortization expense 2020	33,900		33,900
Future amortization expense 2021	28,000		28,000
Future amortization expense 2022	$ 22,400		$ 22,400