Goodwill and Acquired Intangible Assets - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of acquired intangible assets	$ 8,431	$ 7,569
Future amortization expense to be recognized in remainder of 2018	24,900
Future amortization expense 2019	36,600
Future amortization expense 2020	33,900
Future amortization expense 2021	28,000
Future amortization expense 2022	$ 22,400