Fair Value Assumptions Used in Probability Weighted Approach and Monte Carlo Simulation Model for Derivatives (Detail) - Series 1 Preferred Stock - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Fair Value Measurement Inputs and 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, Risk Free Interest Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Assumptions of Preferred Stock	1.04%
Measurement Input, Risk Free Interest Rate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Assumptions of Preferred Stock	2.74%	1.92%
Measurement Input, Risk Free Interest Rate | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Assumptions of Preferred Stock		2.12%
Measurement Input, Expected Dividend Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Assumptions of Preferred Stock	0.00%	0.00%
Measurement Input, Price Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Assumptions of Preferred Stock	70.50%
Measurement Input, Price Volatility | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Assumptions of Preferred Stock	82.40%	68.70%
Measurement Input, Price Volatility | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Assumptions of Preferred Stock		80.40%