Net Loss Per Share - Reconciliation of Basic and Diluted Calculation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net loss	$ (8,605)	$ (13,018)	$ (3,438)	$ (12,236)	$ (21,623)	$ (15,674)
Weighted average shares:
Basic shares (in shares)	37,356		36,772		37,355	37,666
Effect of dilutive securities—options and warrants outstanding (in shares)	0		0		0	0
Diluted shares (in shares)	37,356		36,772		37,355	37,666
Net income (loss) per share - basic (in dollars per share)	$ (0.23)		$ (0.09)		$ (0.58)	$ (0.42)
Net income (loss) per share - diluted (in dollars per share)	$ (0.23)		$ (0.09)		$ (0.58)	$ (0.42)