Net loss per share - Summary of Calculation of Diluted Loss Per Share (Detail) - 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
Net loss attributable to common shareholders:
Basic and diluted	$ (38,961)	$ (31,136)	$ (29,077)	$ (13,641)	$ (70,097)	$ (42,718)
Weighted-average common shares outstanding:
Basic and diluted (in shares)	50,788,681		32,837,975		49,737,699	32,431,464
Net loss per common share-basic and diluted (in dollars per share)	$ (0.77)		$ (0.89)		$ (1.41)	$ (1.32)