Net loss per share - Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	8,710	8,382	8,710	8,382
Outstanding stock options (in shares)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	6,099	6,466	6,099	6,466
Restricted stock units (in shares)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	1,865	1,593	1,865	1,593
ESPP shares and other (in shares)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	746	323	746	323