Summary of Significant Accounting Policies - Schedule of Net Loss Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Net loss	$ (20,247)	$ (22,433)	$ (37,654)	$ (26,484)	$ (24,631)	$ (20,545)	$ (18,028)	$ (19,423)	$ (106,818)	$ (82,627)	$ (64,028)
Weighted average common shares outstanding, basic and diluted									40,654,272	25,402,241	19,159,057
Net loss per share attributable to common stockholders	$ (0.41)	$ (0.45)	$ (1.10)	$ (0.91)	$ (0.86)	$ (0.72)	$ (0.73)	$ (0.99)	$ (2.63)	$ (3.25)	$ (3.34)