Net Loss per Share - Potentially Dilutive Securities Excluded from Computation of Diluted Weighted-Average Shares (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents outstanding excluded from diluted earnings per share calculation	12,022,978	10,369,196	12,022,978	10,369,196
Stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents outstanding excluded from diluted earnings per share calculation	10,612,258	7,984,469	10,612,258	7,984,469
ESPP [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents outstanding excluded from diluted earnings per share calculation	54,895		54,895
Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents outstanding excluded from diluted earnings per share calculation	486,812	486,812	486,812	486,812
Restricted stock units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents outstanding excluded from diluted earnings per share calculation	812,347	1,395,829	812,347	1,395,829
Performance Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents outstanding excluded from diluted earnings per share calculation	56,666	466,668	56,666	466,668
Deferred Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents outstanding excluded from diluted earnings per share calculation		35,418		35,418