Restatement of Consolidated Financial Statements - Impact on Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended		9 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	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net loss	$ (5,948)	$ (9,496)	$ (8,296)	$ (6,637)	$ (3,680)	$ (8,495)	$ (8,289)	$ (8,775)	$ (14,933)	$ (17,064)	$ (24,429)	$ (25,559)	$ (30,377)	$ (29,239)
Change in fair value of warrant liability		0	0	0		0	0	0	0	0	0	0	0	0
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net loss		(8,336)	(18,098)	(7,025)		(7,031)	(7,578)	(5,217)	(25,123)	(12,795)	(33,459)	(19,826)	(30,641)	(12,673)
Change in fair value of warrant liability		(1,160)	9,802	388		(1,464)	(711)	(3,558)	10,190	(4,269)	9,030	(5,733)	264	(16,566)
Misapplication of Accounting Guidance for Warrants | Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net loss		(1,160)	9,802	388		(1,464)	(711)	(3,558)	10,190	(4,269)	9,030	(5,733)	264	(16,566)
Change in fair value of warrant liability		$ 1,160	$ (9,802)	$ (388)		$ 1,464	$ 711	$ 3,558	$ (10,190)	$ 4,269	$ (9,030)	$ 5,733	$ (264)	$ 16,566