Equity Instruments - Assumptions for Warrants Issued (Detail)	Mar. 31, 2019 Rate $ / shares shares	Dec. 31, 2018 Rate $ / shares shares	Aug. 31, 2018	Aug. 13, 2018 Rate $ / shares shares
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Number of shares	22,233,191	22,283,191
August 2018 Warrants [Member] | Confidentially Marketed Public Offering
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equivalent term (years)	4 years 4 months 13 days	4 years 7 months 13 days	5 years	5 years
Number of shares	15,500,000	15,600,000		20,000,000
August 2018 Warrants [Member] | Confidentially Marketed Public Offering | Measurement Input, Exercise Price [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and Rights Outstanding, Measurement Input | $ / shares	0.40	0.40		0.40
August 2018 Warrants [Member] | Confidentially Marketed Public Offering | Measurement Input, Price Volatility [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and Rights Outstanding, Measurement Input	130.2	129.8		121.8
August 2018 Warrants [Member] | Confidentially Marketed Public Offering | Measurement Input, Risk Free Interest Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and Rights Outstanding, Measurement Input | Rate	2.22	2.50		2.75