Net Income (Loss) per Share - Antidilutive Securities Excluded from Computation of Diluted Net Income (Loss) Per Share of Common Stock (Detail) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	736,073	761,710
Restricted Stock Units for Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	2,665,737	598,503
Employee Share Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	111,357	0