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Stockholders Equity - Additional Information (Detail) (USD $)
 3 Months Ended 3 Months Ended 3 Months Ended 1 Months Ended 12 Months Ended 3 Months Ended 3 Months Ended 12 Months Ended
Mar. 31, 2014
Mar. 31, 2013
Dec. 31, 2013
Mar. 31, 2013
IPO
Mar. 19, 2013
IPO
Mar. 31, 2013
IPO
Overallotment Option
Aug. 31, 2009
2009 Unit Offering
Nov. 30, 2010
2010 Unit Offering
Aug. 31, 2009
Warrant
2009 Unit Offering
Nov. 30, 2010
Warrant
2010 Unit Offering
Dec. 31, 2013
Warrant
2010 Unit Offering
Mar. 31, 2014
Stockholder Rights Plan
Mar. 31, 2014
Sales Agreement
Mlv
Mar. 31, 2014
Sales Agreement
Mlv
Maximum
Mar. 31, 2014
Sales Agreement
Cantor
Dec. 31, 2013
Sales Agreement
Cantor
Stockholders Equity Note [Line Items]                                
Warrants to purchase an aggregate shares of common stock             2,400,000 3,700,000                
Warrant exercise price             2.90 3.20                
Exercisable period                 5 years 5 years            
Warrant liability $ 11,356,000   $ 20,390,000 [1]           $ 2,800,000 $ 5,800,000            
Risk-free interest rate                 2.48% 1.23%            
Expected term (in years)                 5 years 5 years            
Expected dividend yield                 0.00% 0.00%            
Estimated volatility                 77.00% 85.00%            
Net proceeds from underwritten public offering                   19,700,000            
Payment for underwriting discounts and commissions and stock issuance cost       500,000           1,300,000            
Number of units sold in underwritten public offering                   7,400,000            
Number of common stock in each unit                   1            
Number of common stock shares purchasable with each warrant                   0.5            
Units issued, price per unit                   $ 2.85            
Common stock, number of shares issued       8,300,000   1,300,000       7,400,000         0 5,400,000
Warrants exercisable date                   May 15, 2011            
Gain (loss) from revaluation of warrant liability 9,034,000 (5,073,000)                            
Warrants exercised                     186,586          
Maximum common stock offering price                         20,000,000   70,000,000  
Common stock available for sale                           100,000 41,500,000  
Percentage of proceeds payable as compensation to underwriter                             2.00%  
Proceeds from common stock sold 31,000 51,502,000   38,000,000                     0 23,500,000
Common stock, price per share         $ 4.20                      
Gross proceeds from public offering       40,300,000                        
Underwriter's discount       $ 1,800,000                        
Minimum percentage of common stock acquired by stockholders                       15.00%        
Designated preferred stock for future issuance                       250,000        
[1] The financial information in this column was derived from audited financial statements included in the Company's 2013 Annual Report on Form 10-K.