Warrants - Summary of Warrant Activity (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Warrant or Right [Line Items]
Weighted Average Exercise Price, Expired	$ 2.11
Warrants Not Settleable in Cash [Member]
Class of Warrant or Right [Line Items]
Number of Restricted Stock Units Outstanding, Beginning balance	13,162,668	1,426,622	1,426,622
Number of Warrants, Granted		45,769,746
Number of Warrants, Exercised	(8,737,631)	(34,033,700)
Number of Warrants, Expired	(95,600)
Number of Restricted Stock Units Outstanding, Ending balance	4,329,437	13,162,668	1,426,622	1,426,622
Weighted Average Exercise Price, Outstanding, Beginning balance	$ 1.08	$ 1.81	$ 1.81
Weighted Average Exercise Price, Granted		1.00
Weighted Average Exercise Price, Exercised	1.09	1.00
Weighted Average Exercise Price, Expired	1.65
Weighted Average Exercise Price, Outstanding, Ending balance	$ 1.03	$ 1.08	$ 1.81	$ 1.81
Weighted Average Remaining Contractual Life, Outstanding	3 years 8 months 12 days	4 years 6 months	2 years 2 months 12 days	3 years 2 months 12 days
Weighted Average Remaining Contractual Life, Granted		4 years 9 months 18 days
Weighted Average Fair Value, Outstanding, Beginning balance	$ 0.39	$ 1.54	$ 1.54
Weighted Average Fair Value, Granted		0.22
Weighted Average Fair Value, Outstanding, Ending balance	$ 0.26	$ 0.39	$ 1.54	$ 1.54