Summary of Significant Accounting Policies - Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ 107,298	$ 96,829
Cost of revenues	61,133	55,639
Selling and marketing	18,055	$ 16,770
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	108,434
Cost of revenues	61,194
Selling and marketing	18,155
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	(1,136)
Cost of revenues	(61)
Selling and marketing	$ (100)