Net Loss Per Share - Basic Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Basic and diluted net loss per share attributable to common stockholders:
Net loss attributable to common stockholders	$ (36,568)	$ (21,512)	$ (24,453)	$ (17,124)	$ (58,080)	$ (41,577)
Weighted average common shares outstanding, basic and diluted	57,368,292		42,910,084		54,634,572	42,582,501
Net loss per share, basic and diluted	$ (0.64)		$ (0.57)		$ (1.06)	$ (0.98)