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Stockholders' Equity - Additional Information (Detail) (USD $)
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12 Months Ended | 1 Months Ended | 12 Months Ended | 12 Months Ended | |||||||||||||||||||||||
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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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Mar. 16, 2011
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Oct. 29, 2010
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May 31, 2010
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Oct. 05, 2009
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Dec. 31, 2012
August 2008 offering [Member]
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Dec. 31, 2011
August 2008 offering [Member]
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Dec. 31, 2012
October 2009 offering [Member]
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Dec. 31, 2011
October 2009 offering [Member]
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Dec. 31, 2012
March 2011 offering [Member]
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Dec. 31, 2011
March 2011 offering [Member]
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Mar. 16, 2011
March 2011 offering [Member]
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Mar. 16, 2011
March 2011 offering [Member]
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Oct. 05, 2009
October 2009 offering [Member]
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Aug. 29, 2008
August 2008 offering [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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Oct. 29, 2010
Common Stock [Member]
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Dec. 31, 2012
Warrants [Member]
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Dec. 31, 2012
Warrants [Member]
August 2008 offering [Member]
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Dec. 31, 2011
Warrants [Member]
August 2008 offering [Member]
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Dec. 31, 2012
Warrants [Member]
October 2009 offering [Member]
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Dec. 31, 2011
Warrants [Member]
October 2009 offering [Member]
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Dec. 31, 2012
Warrants [Member]
March 2011 offering [Member]
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Dec. 31, 2011
Warrants [Member]
March 2011 offering [Member]
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| Schedule Of Stockholders Equity [Line Items] | |||||||||||||||||||||||||||
| Aggregate offering price of common stock which the Company may issue and sell | $ 15,000,000 | $ 15,000,000 | |||||||||||||||||||||||||
| Aggregate commission rate on gross proceeds | 3.00% | ||||||||||||||||||||||||||
| Common stock sold, shares | 56,431,207 | 49,128,475 | 340,472 | 248,690 | 14,313,081 | 18,324,599 | 8,970,574 | 2,022,144 | 971,037 | ||||||||||||||||||
| Common stock sold, price per share | $ 2.05 | $ 1.86 | $ 2.04 | $ 6.29 | $ 2.66 | ||||||||||||||||||||||
| Net proceeds from sale of common stock | 12,323,000 | 24,007,000 | 27,800,000 | 33,100,000 | 16,800,000 | 12,300,000 | 2,300,000 | ||||||||||||||||||||
| Warrants exercisable, price per unit of warrant | $ 0.05 | $ 0.05 | |||||||||||||||||||||||||
| Warrants issued | 136,186 | 99,475 | 5,725,227 | 7,329,819 | 3,588,221 | ||||||||||||||||||||||
| Gross proceed from sale of common stock | 30,100,000 | 35,000,000 | 18,300,000 | ||||||||||||||||||||||||
| Term of warrants | 5 years | 5 years | 5 years | ||||||||||||||||||||||||
| Warrant exercise price | 2.46 | 2.23 | |||||||||||||||||||||||||
| Warrant, reduced exercise price | $ 2.05 | $ 1.86 | |||||||||||||||||||||||||
| Warrant, original exercise price | $ 2.34 | ||||||||||||||||||||||||||
| Common stock, shares authorized | 150,000,000 | 150,000,000 | 50,000,000 | ||||||||||||||||||||||||
| Warrants exercised | 5,060,433 | ||||||||||||||||||||||||||
| Proceeds from warrants exercises | 8,800,000 | ||||||||||||||||||||||||||
| Reclassification of fair value from liability to permanent equity of warrants exercised | 27,900,000 | ||||||||||||||||||||||||||
| Warrants outstanding | 11,600,000 | 3,058,811 | 3,588,221 | 4,287,940 | 7,329,819 | 4,236,083 | 5,725,227 | ||||||||||||||||||||
| Change in fair value of common stock warrants | (9,900,000) | 1,100,000 | (24,200,000) | 1,400,000 | (17,100,000) | 1,900,000 | |||||||||||||||||||||
| Fair value of warrants | $ 6,100,000 | ||||||||||||||||||||||||||
| Distribution rate under Preferred Share Rights Agreement | One right for each share of common stock held | ||||||||||||||||||||||||||
| Minimum acquisition percentage of outstanding shares for rights to become exercisable | 15.00% | ||||||||||||||||||||||||||
| Purchase price per right | $ 25.00 | ||||||||||||||||||||||||||
| Redeemable price per right | $ 0.01 | ||||||||||||||||||||||||||
| Preferred stock reserved | 200,000 | ||||||||||||||||||||||||||
| Preferred share rights expiration date | August 8, 2016 | ||||||||||||||||||||||||||