Key Assumptions Used to Value the PIPE Warrants (Detail) - PIPE Warrants [Member] - $ / shares	1 Months Ended	12 Months Ended
	May 31, 2016	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Expected price volatility	76.25%	78.18%
Expected term (in years)	5 years	4 years 6 months
Risk-free interest rates	1.22%	1.93%
Stock price	$ 0.89	$ 0.54