Derivative Instruments (Tables)

9 Months Ended

Sep. 30, 2013

Derivative Instruments And Hedging Activities Disclosure [Abstract]

Changes in Derivative Warrant Liability

The table below presents the changes in derivative warrant liability for the nine months ended September 30:

	Nine Months Ended September 30,
	2013			2012
Balance at December 31,	$	14,584,818		$	35,473,230
Increase (decrease) in the fair value of the warrants		18,871,329			(21,436,653	)
Reduction in derivative liability due to exercise and modification of warrants		(33,456,147	)		(3,235,722	)
Balance at September 30,	$	—		$	10,800,855