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Gain Loss on Derivative Instruments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		190 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended			6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2012 Investor warrants expiring April 30, 2015	Jun. 30, 2011 Investor warrants expiring April 30, 2015	Jun. 30, 2012 Investor warrants expiring April 30, 2015	Jun. 30, 2011 Investor warrants expiring April 30, 2015	Jun. 30, 2012 Investor warrants expiring March 29, 2016	Jun. 30, 2011 Investor warrants expiring March 29, 2016	Jun. 30, 2012 Investor warrants expiring March 29, 2016	Jun. 30, 2011 Investor warrants expiring March 29, 2016	Jun. 30, 2012 Rights Offering Derivative	Jun. 30, 2011 Rights Offering Derivative	Mar. 31, 2011 Rights Offering Derivative	Jun. 30, 2012 Rights Offering Derivative	Jun. 30, 2011 Rights Offering Derivative	Jun. 30, 2012 Options to Contractors	Jun. 30, 2011 Options to Contractors	Jun. 30, 2012 Options to Contractors	Jun. 30, 2011 Options to Contractors
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized/realized gain (loss) on derivatives	$ 645	$ 225	$ 3,971	$ 5,905	$ 8,792	$ 513	$ 154	$ 2,981	$ 5,221	$ 125	$ 71	$ 946	$ 71	$ 0	$ 0	$ 613	$ 0	$ 613	$ 7	$ 0	$ 44	$ 0