Net Income (Loss) Per Share Attributable to Common Stockholders - Additional Information (Detail) - shares	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Stock Option [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Number of anti-dilutive securities excluded from computation of earnings per share	2,400,000
Weighted Average [Member] | Stock Option [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Number of anti-dilutive securities excluded from computation of earnings per share	100,000	3,348,632	898,962
Weighted Average [Member] | Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Number of anti-dilutive securities excluded from computation of earnings per share	300,000	317,562	317,562