Stock-based compensation - Summary of Stock Option Activity Under Plan (Detail) - $ / shares shares in Thousands	9 Months Ended
	Sep. 30, 2021
Shares (in thousands)
Outstanding at beginning of period (in shares)	6,262
Granted (in shares)	1,188
Exercised (in shares)	(219)
Canceled, forfeited, or expired (in shares)	(1,557)
Outstanding at end of period (in shares)	5,674
Exercisable at end of period (in shares)	3,527
Vested and expected to vest at end of period (in shares)	5,373
Weighted- average exercise price per share
Outstanding at beginning of period (in dollars per share)	$ 105.02
Granted (in dollars per share)	27.85
Exercised (in dollars per share)	6.82
Canceled, forfeited, or expired (in dollars per share)	104.89
Outstanding at end of period (in dollars per share)	92.68
Exercisable at end of period (in dollars per share)	111.09
Vested and expected to vest at end of period (in dollars per share)	$ 92.68