Stock-based compensation - Summary of Stock Option Activity Under Plan (Detail) shares in Thousands	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Shares (in thousands)
Outstanding at beginning of period (in shares) | shares	5,483
Granted (in shares) | shares	1,147
Exercised (in shares) | shares	(20)
Canceled, forfeited, or expired (in shares) | shares	(132)
Outstanding at end of period (in shares) | shares	6,478
Exercisable at end of period (in shares) | shares	3,248
Vested and expected to vest at end of period (in shares) | shares	6,478
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 116.30
Granted (in dollars per share) | $ / shares	75.65
Exercised (in dollars per share) | $ / shares	37.71
Canceled, forfeited, or expired (in dollars per share) | $ / shares	148.55
Outstanding at end of period (in dollars per share) | $ / shares	108.68
Exercisable at end of period (in dollars per share) | $ / shares	99.92
Vested and expected to vest at end of period (in dollars per share) | $ / shares	$ 108.68