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Stockholders' Equity - Additional Information (Detail) (USD $)
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3 Months Ended | 9 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | ||||||||||
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Sep. 30, 2012
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Sep. 30, 2012
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Sep. 30, 2011
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Jan. 20, 2012
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Dec. 31, 2011
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Sep. 30, 2012
August 2008 Offering [Member]
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Dec. 31, 2011
August 2008 Offering [Member]
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Sep. 30, 2012
October 2009 Offering [Member]
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Dec. 31, 2011
October 2009 Offering [Member]
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Sep. 30, 2012
March 2011 Offering [Member]
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Dec. 31, 2011
March 2011 Offering [Member]
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Sep. 30, 2012
Common Stock [Member]
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Mar. 31, 2012
Common Stock [Member]
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Sep. 30, 2012
Warrant [Member]
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Sep. 30, 2012
Warrant [Member]
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Sep. 30, 2012
Warrant [Member]
August 2008 Offering [Member]
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Sep. 30, 2012
Warrant [Member]
August 2008 Offering [Member]
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Sep. 30, 2012
Warrant [Member]
October 2009 Offering [Member]
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Sep. 30, 2012
Warrant [Member]
October 2009 Offering [Member]
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Sep. 30, 2012
Warrant [Member]
March 2011 Offering [Member]
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Sep. 30, 2012
Warrant [Member]
March 2011 Offering [Member]
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| Schedule Of Stockholders Equity [Line Items] | |||||||||||||||||||||
| Common stock having aggregate price of up to | $ 15,000,000 | ||||||||||||||||||||
| Common stock sold, shares | 56,216,122 | 56,216,122 | 49,128,475 | 2,022,144 | |||||||||||||||||
| Common stock sold, price per share | $ 6.29 | ||||||||||||||||||||
| Net proceeds from sale of common stock | 12,300,000 | ||||||||||||||||||||
| Warrants Exercised | 872,451 | 4,584,474 | |||||||||||||||||||
| Proceeds from warrant exercises | 1,600,000 | 8,500,000 | |||||||||||||||||||
| Reclassification of fair value from liability to permanent equity of warrants exercised | 5,400,000 | 27,400,000 | |||||||||||||||||||
| Warrants outstanding | 11,700,000 | 11,700,000 | 3,058,811 | 3,588,221 | 4,287,940 | 7,329,819 | 4,378,940 | 5,725,227 | |||||||||||||
| Change in fair value of common stock warrants | $ (85,572,000) | $ 1,538,000 | $ 500,000 | $ 19,000,000 | $ 700,000 | $ 36,800,000 | $ 1,700,000 | $ 29,800,000 | |||||||||||||