Significant Accounting Policies - Impacts on Statements of Comprehensive Loss from the Adoption of ASC 606 (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net loss	$ (10,797)	$ (14,650)	$ (10,051)	$ (15,216)	$ (13,903)	$ (15,028)	$ (10,967)	$ (9,553)	$ (50,714)	$ (49,451)	$ (31,007)
Foreign currency translation adjustment									(827)	103	(891)
Total other comprehensive loss, net of income taxes									(51,541)	$ (49,348)	$ (31,898)
Calculated under Revenue Guidance in Effect before Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net loss									(49,391)
Foreign currency translation adjustment									(942)
Total other comprehensive loss, net of income taxes									(50,333)
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net loss									(1,323)
Foreign currency translation adjustment									115
Total other comprehensive loss, net of income taxes									$ (1,208)