Significant Accounting Policies - Summary of Basic and Diluted Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017
Numerator
Net loss	$ (12,040)	$ (28,024)
Denominator
Weighted-average common shares outstanding - basic and diluted	16,671,019	18,632,740
Basic and diluted net loss per share	$ (0.72)	$ (1.50)