Net Loss per Share - Potentially Dilutive Securities Excluded from Computation of Diluted Weighted-Average Shares (Detail) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 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	13,717,898	30,321,078	13,717,898	30,321,078
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	11,552,639	7,750,244	11,552,639	7,750,244
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	20,671,036	486,812	20,671,036
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	1,376,364	1,398,129	1,376,364	1,398,129
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	301,666	466,668	301,666	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	417	35,001	417	35,001