Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Observable Inputs (Level 2) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Change in fair value included in earnings	$ (124,000)	$ 3,062,575	$ (1,448,819)
Fair Value, Measurements, Recurring | Warrants | Fair Value, Inputs, Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Balance	615,000	8,682,441	14,275,483
Change in fair value included in earnings	124,000	(3,062,575)	1,448,819
Exercise of warrants	(385,000)	(5,004,866)	(7,041,861)
Balance	$ 354,000	$ 615,000	$ 8,682,441