Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Observable Inputs (Level 2) (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Change in fair value included in earnings	$ (108,000)	$ (430,000)
Fair Value, Measurements, Recurring | Warrants | Fair Value, Inputs, Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Balance	354,000
Change in fair value included in earnings	108,000
Exercise of warrants	0
Balance	$ 462,000