Summary of Significant Accounting Policies - Recent Accounting Pronouncements Narrative (Details) - USD ($) $ in Thousands	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit		$ (351,084)	$ (318,235)
Forecast | Accelerated revenue component | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit	$ (3,000)
Forecast | Capitalized sales commission component | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit	$ (3,000)
Forecast | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Commissions amortization period	3 years