Fair Value Measurement - Roll Forward for Financial Assets and Liabilities Measured at Fair Value Using Significant Other Observable Inputs (Level 2) (Detail) (Fair Value, Measurements [Member], USD $)

9 Months Ended

Sep. 30, 2013

Significant Other Observable Inputs Level 2 [Member]

Sep. 30, 2013

Significant Other Observable Inputs Level 2 [Member]

Bond obligation [Member]

Sep. 30, 2013

Significant Other Observable Inputs Level 2 [Member]

Warrant liabilities [Member]

Sep. 30, 2013

Significant Other Observable Inputs Level 2 [Member]

Marketable securities [Member]

Dec. 31, 2012

Significant Other Observable Inputs Level 2 [Member]

Marketable securities [Member]

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Marketable debt securities, Beginning Balance

$ 20,955,293

$ 331,250

$ 107,968

$ 13,900,678

Fair Value Measurement With Unobservable inputs reconciliation recurring basis asset transfers into level 1

(13,900,678)

Financial liabilities change included in earning fair value disclosure

(92,708)

Financial liabilities change settled in earning fair value disclosure

(152,500)

Marketable debt securities, ending Balance

$ 20,955,293

$ 178,750

$ 15,260

$ 13,900,678

Fair Value Measurement - Roll Forward for Financial Assets and Liabilities Measured at Fair Value Using Significant Other Observable Inputs (Level 2) (Detail) (Fair Value, Measurements [Member], USD $)			9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013 Significant Other Observable Inputs Level 2 [Member]	Sep. 30, 2013 Significant Other Observable Inputs Level 2 [Member] Bond obligation [Member]	Sep. 30, 2013 Significant Other Observable Inputs Level 2 [Member] Warrant liabilities [Member]	Sep. 30, 2013 Significant Other Observable Inputs Level 2 [Member] Marketable securities [Member]	Dec. 31, 2012 Significant Other Observable Inputs Level 2 [Member] Marketable securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable debt securities, Beginning Balance	$ 20,955,293		$ 331,250	$ 107,968		$ 13,900,678
Fair Value Measurement With Unobservable inputs reconciliation recurring basis asset transfers into level 1					(13,900,678)
Financial liabilities change included in earning fair value disclosure				(92,708)
Financial liabilities change settled in earning fair value disclosure			(152,500)
Marketable debt securities, ending Balance	$ 20,955,293		$ 178,750	$ 15,260		$ 13,900,678