Loss per Share - Two Class Method (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Loss per Share
Net loss	$ (10,579)	$ (183)	$ (20,350)	$ (6,593)
Less: preferred dividends	(1,892)	(1,382)	(5,548)	(4,099)
Net loss attributable to stockholders	(12,471)	(1,565)	(25,898)	(10,692)
Net loss attributable to common stockholders (Note 11)	$ (12,471)	$ (1,565)	$ (25,898)	$ (10,692)
Denominator:
Weighted average common shares outstanding (in shares)	14,085	13,322	13,873	13,306
Loss per common share - basic and diluted under two-class method (in dollars per share)	$ (0.89)	$ (0.12)	$ (1.87)	$ (0.80)