Net Loss Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Basic and diluted net loss per common share calculation:
Net loss	$ (25,450)	$ (18,589)	$ (15,076)	$ (14,437)	$ (14,443)	$ (12,501)	$ (59,115)	$ (41,381)
Weighted average common shares outstanding - basic and dilutive (in shares)	92,675			41,552			67,931	41,486
Basic and diluted (in dollars per share)	$ (0.27)			$ (0.35)			$ (0.87)	$ (1.00)
Anti-dilutive securities
Total (in shares)	9,153			6,163			9,153	6,163
Stock options outstanding
Anti-dilutive securities
Total (in shares)	7,426			5,468			7,426	5,468
Restricted stock units
Anti-dilutive securities
Total (in shares)	1,727			695			1,727	695