Net Loss per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Net loss per share - Basic:
Net loss	$ (24,226)	$ 8,817	$ (11,176)	$ (10,974)	$ (15,409)	$ (22,150)
Denominator for basic net loss per share	33,583		28,461		31,941	28,070
Basic net loss per common share	$ (0.72)		$ (0.39)		$ (0.48)	$ (0.79)
Net loss per share - Diluted:
Net loss	$ (24,226)	$ 8,817	$ (11,176)	$ (10,974)	$ (15,409)	$ (22,150)
Less: Future tranche right revaluation gain applicable to dilutive liability-classified future tranche rights					(2,284)
Numerator for diluted net loss per share	$ (24,226)		$ (11,176)		$ (17,693)	$ (22,150)
Denominator for basic net loss per share	33,583		28,461		31,941	28,070
Plus: Incremental shares underlying "in the money" liability-classified future tranche rights outstanding					2,182
Denominator for diluted net loss per share	33,583		28,461		34,123	28,070
Diluted net loss per common share	$ (0.72)		$ (0.39)		$ (0.52)	$ (0.79)