Equity Instruments - Warrants Issued in Conjunction with its Senior Convertible Debentures (Detail) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Number of Warrants Outstanding
Number of Warrants Outstanding, Beginning Balance	22,283,191
Number of Warrants, Warrants exercised	(50,000)
Number of Warrants Outstanding, Ending Balance	22,233,191	22,283,191
Warrants, Weighted Average Exercise Price
Weighted Average Exercise Price, Outstanding Beginning Balance	$ 0.51
Weighted Average Exercise Price, Warrants exercised	0.40
Weighted Average Exercise Price, Outstanding Ending Balance	$ 0.51	$ 0.51
Weighted Average Remaining Contractual Life
Weighted Average Remaining Contractual Life, Warrants Outstanding	4 years	4 years 3 months