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
Basic and diluted net loss per common share calculation:
Net loss	$ (18,589)	$ (15,076)	$ (14,443)	$ (12,501)	$ (33,665)	$ (26,944)
Weighted average common shares outstanding - basic and dilutive (in shares)	57,421		41,477		55,424	41,452
Basic and diluted (in dollars per share)	$ (0.32)		$ (0.35)		$ (0.61)	$ (0.65)
Anti-dilutive securities
Total (in shares)	8,791		6,325		8,791	6,325
Stock options outstanding
Anti-dilutive securities
Total (in shares)	7,155		5,690		7,155	5,690
Restricted stock units
Anti-dilutive securities
Total (in shares)	1,636		635		1,636	635