Goodwill and Acquired Intangible Assets - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of acquired intangible assets	$ 9,599	$ 8,431
Future amortization expense to be recognized in remainder of 2019	38,400
Future amortization expense 2020	36,700
Future amortization expense 2021	31,700
Future amortization expense 2022	26,000
Future amortization expense 2023	$ 20,100