Net Loss Per Share - Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net loss attributable to common stockholders	$ (24,081)	$ (16,394)	$ (43,701)	$ (28,468)
Denominator:
Weighted‑average common shares outstanding—basic and diluted (in shares)	96,785,915	44,855,083	95,754,714	41,668,902
Net loss per share attributable to common stockholders—basic and diluted (in dollars per share)	$ (0.25)	$ (0.37)	$ (0.46)	$ (0.68)