Net Loss Per Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Net Loss Per Share
Common stock, outstanding shares	12,354,014	0
Numerator:
Net loss	$ (29,727)	$ (25,632)
Accretion of preferred stock to redemption value	(244)
Net loss attributable to common stockholders	(29,971)
Less change in fair value of warrant liability	473
Net loss attributable to common stockholders for diluted loss per share	$ (30,444)
Denominator:
Weighted average number of common shares outstanding - basic	9,161,844
Assumed conversion of dilutive securities:
Private Placement Warrants	26,743
Denominator for diluted loss per share - adjusted weighted average shares	9,188,587
Net loss per share attributable to common stockholders - basic	$ (3.27)
Net loss per share attributable to common stockholders - diluted	$ (3.31)