Revenue Recognition - Cumulative Effect of Changes to Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Other accrued liabilities		$ 4,893
Accumulated deficit	$ (102,495)	(102,467)	$ (102,672)	$ (92,223)	$ (74,835)
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Other accrued liabilities			5,098
Accumulated deficit			$ (102,503)
Adjustments Upon Adoption of ASC 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Other accrued liabilities		(205)
Accumulated deficit		$ 205