Summary of Warrant Activity (Detail) - Warrants - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shares
Beginning Balance	10,093,836	10,093,836	1,697,974
Granted	2,035,398		9,205,862
Exercised			(200,000)
Forfeited, cancelled, or expired	(722,974)		(610,000)
Ending Balance	11,406,260	10,093,836	10,093,836
Warrants exercisable, December 31, 2016	9,235,862
Weighted-Average Exercise Price Per Share
Beginning Balance	$ 4.18	$ 4.18	$ 5.44
Granted	2.00		4.00
Exercised			2.00
Forfeited, cancelled, or expired	6.50		5.71
Ending Balance	3.64	$ 4.18	$ 4.18
Warrants exercisable, December 31, 2016	$ 4.00