Net Loss Per Common Share - Narrative (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
Numerator:
Net loss	$ (19,792)	$ (2,844)	$ (4,651)	$ (7,659)	$ (22,636)	$ (12,310)
Denominator for basic and diluted EPS:
Weighted-average common shares outstanding (in shares)	43,956		38,349		43,841	37,251
Net loss per share attributable to common shareholders (basic and diluted) (in dollars per share)	$ (0.45)		$ (0.12)		$ (0.52)	$ (0.33)
Options
Denominator for basic and diluted EPS:
Aggregate number of common equivalent shares (related to options, warrants and preferred stock) excluded from diluted net loss per common share (in shares)					5,600	5,400
Restricted Stock
Denominator for basic and diluted EPS:
Aggregate number of common equivalent shares (related to options, warrants and preferred stock) excluded from diluted net loss per common share (in shares)					200
Warrants Amounts
Denominator for basic and diluted EPS:
Aggregate number of common equivalent shares (related to options, warrants and preferred stock) excluded from diluted net loss per common share (in shares)					100	400