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Common Stock - Additional Information (Detail) (USD $)
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9 Months Ended | 1 Months Ended | 9 Months Ended | 1 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 1 Months Ended | |||||||||||||
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Sep. 30, 2014
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Sep. 30, 2013
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Sep. 30, 2013
Common Stock [Member]
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Sep. 30, 2014
Restricted Stock [Member]
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Feb. 28, 2014
Executive Vice Chairman [Member]
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Dec. 19, 2013
Executive Vice Chairman [Member]
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Feb. 20, 2014
Executive Vice Chairman [Member]
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Sep. 30, 2014
Executive Vice Chairman [Member]
Share-based Compensation Award, Tranche One [Member]
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Sep. 30, 2014
Executive Vice Chairman [Member]
Share-based Compensation Award, Tranche Two [Member]
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Sep. 30, 2014
Executive Vice Chairman [Member]
Share-based Compensation Award, Tranche Three [Member]
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Dec. 19, 2013
Executive Vice Chairman [Member]
Restricted Stock [Member]
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Sep. 30, 2014
Executive Vice Chairman [Member]
Restricted Stock [Member]
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Sep. 30, 2014
Director [Member]
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Sep. 30, 2014
Board Of Directors [Member]
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Sep. 30, 2014
Research and Development Expense [Member]
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Sep. 30, 2013
Research and Development Expense [Member]
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Sep. 30, 2014
Research and Development Expense [Member]
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Sep. 30, 2013
Research and Development Expense [Member]
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Sep. 30, 2014
General and Administrative Expense [Member]
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Sep. 30, 2013
General and Administrative Expense [Member]
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Sep. 30, 2014
General and Administrative Expense [Member]
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Sep. 30, 2013
General and Administrative Expense [Member]
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Apr. 30, 2013
2013 ATM [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||||||||||||||||||||||
| Stock Issued During Period, Value, Other | $ 45,000,000 | ||||||||||||||||||||||
| Professional Fees | 32,000 | ||||||||||||||||||||||
| Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options | 1,500,000 | ||||||||||||||||||||||
| Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options | 16,400,000 | ||||||||||||||||||||||
| Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition | 9 months 18 days | 3 years 3 months 18 days | |||||||||||||||||||||
| Stock Issued During Period Shares warrants Exercised | 80,705 | 340 | |||||||||||||||||||||
| Cash Less Exercise Of Warrants | 158,429 | ||||||||||||||||||||||
| Warrants Exercise Price | $ 5.02 | ||||||||||||||||||||||
| Allocated Share-based Compensation Expense | 300,000 | 600,000 | 900,000 | 2,100,000 | 700,000 | 1,200,000 | 3,200,000 | 2,000,000 | |||||||||||||||
| Officers Compensation | 28,275 | ||||||||||||||||||||||
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 3,958,692 | 1,979,346 | 30,000 | 50,000 | |||||||||||||||||||
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value | 3,800,000 | 10,600,000 | 500,000 | ||||||||||||||||||||
| Share Price | $ 1.93 | $ 2.69 | $ 2.69 | $ 2.69 | |||||||||||||||||||
| Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | 16.67% | 50.00% | 10.00% | ||||||||||||||||||||
| Stock Issued During Period, Value, Restricted Stock Award, Gross | 80,700 | ||||||||||||||||||||||
| Proceeds From Issuance Of Common Stock | $ 606,000 | $ 90,629,000 | $ 1,098 | ||||||||||||||||||||