Net Loss Per Share - Summary of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Numerator:
Net loss	$ (107,245)	$ (95,764)	$ (136,347)	$ (126,740)	$ (203,009)	$ (263,087)
Denominator:
Weighted average common stock outstanding —basic	58,582,569		51,926,074		58,478,970	51,917,417
Dilutive effect of shares of common stock equivalents resulting from common stock options and restricted stock units	0		0		0	0
Weighted average common stock outstanding —diluted	58,582,569		51,926,074		58,478,970	51,917,417
Net loss per share—basic and diluted	$ (1.83)		$ (2.63)		$ (3.47)	$ (5.07)