Warrants - Summary of Change in Warrant (Detail) - Warrants Not Settleable in Cash [Member] - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Class of Warrant or Right [Line Items]
Number of Warrants, Outstanding, Beginning balance	13,162,668
Number of Warrants, Exercised	(4,537,722)
Number of Warrants, Cancelled	(95,600)
Number of Warrants, Outstanding, Ending balance	8,529,346	13,162,668
Weighted Average Exercise Price, Outstanding, Beginning balance	$ 1.08
Weighted Average Exercise Price, Exercised	1.11
Weighted Average Exercise Price, Cancelled	1.65
Weighted Average Exercise Price, Outstanding, Ending balance	$ 1.05	$ 1.08
Weighted Average Remaining Contractual Life, Outstanding	4 years 6 months	4 years 6 months
Weighted Average Grant Date Fair Value, Outstanding, Beginning balance	$ 0.39
Weighted Average Grant Date Fair Value, Outstanding, Ending balance	$ 0.40	$ 0.39