Stockholders' Equity - Additional Information (Detail) (USD $)
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12 Months Ended | 0 Months Ended | 12 Months Ended | 0 Months Ended | 12 Months Ended | 12 Months Ended | 12 Months Ended | ||||||||||||||||||||||||
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Dec. 31, 2013
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Dec. 31, 2012
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Dec. 31, 2011
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Jan. 20, 2012
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Oct. 29, 2010
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Oct. 05, 2009
October 2009 Offering [Member]
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Dec. 31, 2013
Warrants [Member]
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Dec. 31, 2012
Warrants [Member]
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Dec. 31, 2012
Common Stock [Member]
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Dec. 31, 2011
Common Stock [Member]
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Dec. 31, 2013
Common Stock [Member]
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Oct. 29, 2010
Common Stock [Member]
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Mar. 16, 2011
March 2011 Offering [Member]
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Aug. 29, 2008
August 2008 Offering [Member]
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Dec. 31, 2013
August 2008 Offering [Member]
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Dec. 31, 2012
August 2008 Offering [Member]
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Dec. 31, 2013
August 2008 Offering [Member]
Warrants [Member]
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Dec. 31, 2012
August 2008 Offering [Member]
Warrants [Member]
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Dec. 31, 2011
August 2008 Offering [Member]
Warrants [Member]
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Dec. 31, 2013
Cashless Exercise of Warrants [Member]
Warrants [Member]
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Dec. 31, 2012
Cashless Exercise of Warrants [Member]
Warrants [Member]
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Dec. 31, 2013
October 2009 Offering [Member]
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Dec. 31, 2012
October 2009 Offering [Member]
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Dec. 31, 2013
October 2009 Offering [Member]
Warrants [Member]
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Dec. 31, 2012
October 2009 Offering [Member]
Warrants [Member]
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Dec. 31, 2011
October 2009 Offering [Member]
Warrants [Member]
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Dec. 31, 2013
March 2011 Offering [Member]
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Dec. 31, 2012
March 2011 Offering [Member]
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Dec. 31, 2013
March 2011 Offering [Member]
Warrants [Member]
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Dec. 31, 2012
March 2011 Offering [Member]
Warrants [Member]
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Dec. 31, 2011
March 2011 Offering [Member]
Warrants [Member]
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Class of Warrant or Right [Line Items] | |||||||||||||||||||||||||||||||
Aggregate offering price of common stock which the Company may issue and sell | $ 2,700,000 | $ 15,000,000 | $ 15,000,000 | ||||||||||||||||||||||||||||
Aggregate commission rate on gross proceeds | 3.00% | ||||||||||||||||||||||||||||||
Common stock sold, shares | 59,232,611 | 56,431,207 | 18,324,599 | 2,022,144 | 971,037 | 0 | 14,313,081 | 8,970,574 | |||||||||||||||||||||||
Common stock sold, price per share | $ 1.86 | $ 6.29 | $ 2.66 | $ 2.05 | $ 2.04 | ||||||||||||||||||||||||||
Net proceeds from sale of common stock | 12,323,000 | 24,007,000 | 33,100,000 | 12,300,000 | 2,300,000 | 27,800,000 | 16,800,000 | ||||||||||||||||||||||||
Warrants exercisable, price per unit of warrant | $ 0.05 | $ 0.05 | |||||||||||||||||||||||||||||
Warrants issued | 7,329,819 | 5,725,227 | 3,588,221 | ||||||||||||||||||||||||||||
Gross proceed from sale of common stock | 35,000,000 | 30,100,000 | 18,300,000 | ||||||||||||||||||||||||||||
Term of warrants | 5 years | 5 years | 5 years | ||||||||||||||||||||||||||||
Warrant exercise price | 2.23 | 2.46 | |||||||||||||||||||||||||||||
Warrant, reduced exercise price | $ 2.05 | $ 1.86 | |||||||||||||||||||||||||||||
Warrant, original exercise price | $ 2.34 | ||||||||||||||||||||||||||||||
Warrants exercised | 933,475 | 4,060,538 | 2,367,636 | 999,895 | |||||||||||||||||||||||||||
Net proceeds from warrants exercised | 1,900,000 | 8,800,000 | |||||||||||||||||||||||||||||
Common stock shares issued for cashless conversion of warrants | 1,555,043 | 666,793 | |||||||||||||||||||||||||||||
Reclassification of fair value from liability to permanent equity of warrants exercised | 11,500,000 | 27,900,000 | |||||||||||||||||||||||||||||
Warrants outstanding | 8,300,000 | 0 | 3,058,811 | 4,287,940 | 4,287,940 | 3,993,783 | 4,236,083 | ||||||||||||||||||||||||
Change in fair value of common stock warrants | $ 2,400,000 | $ 9,900,000 | $ 1,100,000 | $ 600,000 | $ 24,200,000 | $ 1,400,000 | $ 500,000 | $ 17,100,000 | $ 1,900,000 |