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Derivative Instruments - Summary of Changes in Derivative Warrant Liability (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Balance at beginning of the period			$ 14,584,818	$ 35,473,230
Increase (decrease) in the fair value of the warrants	(8,422,513)	4,954,238	18,871,329	(10,567,444)
Reduction in derivative liability due to exercise and modification of warrants			(33,456,147)	(1,377,904)
Balance at end of the period	$ 0	$ 23,527,882	$ 0	$ 23,527,882

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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