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Warrant Liability - Summary of Changes in Fair Value of Warrant Liability (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014
Class of Warrant or Right [Line Items]
Number of Warrants, ending balance	7,336,880
Series A Warrants [Member]
Class of Warrant or Right [Line Items]
Number of Warrants, beginning balance	8,116,895
Number of Warrants, Less exercised	(1,180,015)
Number of Warrants, changes in fair value	0
Number of Warrants, ending balance	6,936,880
Fair value of warrant liability, beginning balance	$ 5,541,809
Fair value of warrants exercised	(1,434,807)
Fair value, changes in fair value at period end	(2,422,451)
Fair value of warrant liability, ending balance	$ 1,684,551