Purchased Intangible Assets - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Purchased Intangible Assets [Abstract]
Intangible asset amortization expense	$ 380	$ 505
Future amortization expense, Remainder of 2018	1,146
Future amortization expense, 2019	1,527
Future amortization expense, 2020	1,325
Future amortization expense, 2021	577
Future amortization expense, 2022	511
Future amortization expense, 2023	$ 494