Derivative Instruments - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Derivative Instruments And Hedging Activities [Line Items]
Warrants exercised	11,726,343
Fair value of warrants	$ 26,006,170
Expiration date of new warrants extended			2 years
Merger warrants to purchase common stock	3,319,091		3,319,091
Increase in derivative warrant liability			764,769
Fair value of warrants			7,738,320
Warrants outstanding	3,674,444		3,674,444
Derivative instruments, fair value	0	23,527,882	0	23,527,882	14,584,818	35,473,230
Warrant derivative gains (losses)	$ (8,422,513)	$ 4,954,238	$ 18,871,329	$ (10,567,444)
Merger Warrants [Member]
Derivative Instruments And Hedging Activities [Line Items]
Merger warrants to purchase common stock	255,000		255,000
Placement Agent Warrants [Member]
Derivative Instruments And Hedging Activities [Line Items]
Merger warrants to purchase common stock	3,064,091		3,064,091