Dilutive Shares Which Could Exist Pursuant to Exercise of Outstanding Stock Instruments and Which were not Included in Calculation (Detail) - shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive shares not included in calculation	18,769,789	21,218,760
Warrant
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive shares not included in calculation	10,697,026	12,249,590
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive shares not included in calculation	3,764,648	4,656,888
Contingently Issuable Shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive shares not included in calculation	4,308,115	4,312,282