Stock-based compensation - Summary of Stock Option Activity Under Plan (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares
Shares (in thousands)
Outstanding at beginning of period (in shares) | shares	5,483
Granted (in shares) | shares	1,585
Exercised (in shares) | shares	(95)
Canceled or forfeited (in shares) | shares	(711)
Outstanding at end of period (in shares) | shares	6,262
Exercisable at end of period (in shares) | shares	3,669
Vested and expected to vest at end of period (in shares) | shares	6,262
Weighted- average exercise price per share
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 116.30
Granted (in dollars per share) | $ / shares	69.40
Exercised (in dollars per share) | $ / shares	19.43
Canceled or forfeited (in dollars per share) | $ / shares	124.00
Outstanding at end of period (in dollars per share) | $ / shares	105.02
Exercisable at end of period (in dollars per share) | $ / shares	107.11
Vested and expected to vest at end of period (in dollars per share) | $ / shares	$ 105.02
Weighted- average contractual life (in years)
Outstanding at end of period	7 years
Exercisable at end of period	5 years 9 months 18 days
Vested and expected to vest at end of period	7 years
Aggregate intrinsic value (in thousands)
Outstanding at end of period | $	$ 15,716
Exercisable at end of period | $	15,659
Vested and expected to vest at end of period | $	$ 15,716