Fair Value Assumptions Used in Probability Weighted Approach and Monte Carlo Simulation Model for Derivatives (Detail) - Series 1 Preferred Stock - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Preferred stock conversion limit - percentage of outstanding common stock	19.90%	19.90%
Preferred conversion floor price	$ 1.00	$ 1.00
Measurement Input, Expected Dividend Rate [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions of Preferred Stock	0.00%	0.00%
Minimum | Measurement Input, Risk Free Interest Rate [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions of Preferred Stock	2.50%	1.92%
Minimum | Measurement Input, Price Volatility [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions of Preferred Stock	77.60%	68.70%
Maximum | Measurement Input, Risk Free Interest Rate [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions of Preferred Stock	3.13%	2.12%
Maximum | Measurement Input, Price Volatility [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions of Preferred Stock	82.40%	80.40%