Net Loss per Share Attributable to Common Stockholders - Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Detail) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from computation of net loss per share	2,476,521	9,887,412	2,476,521	9,887,412
Redeemable Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from computation of net loss per share		8,577,571		8,577,571
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from computation of net loss per share	2,453,259	1,309,841	2,453,259	1,309,841
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from computation of net loss per share	23,262	0	23,262	0