Annual report pursuant to Section 13 and 15(d)

Capital Stock, Other Offerings and Agreements (Details)

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Capital Stock, Other Offerings and Agreements (Details) (USD $)
12 Months Ended 1 Months Ended 11 Months Ended 12 Months Ended 11 Months Ended 12 Months Ended 1 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Jun. 30, 2009
Registered Direct Offerings [Member]
May 31, 2011
2010 ATM Agreement [Member]
Dec. 31, 2011
2010 ATM Agreement [Member]
Dec. 31, 2011
2011 ATM Agreement [Member]
Dec. 31, 2013
2011 ATM Agreement [Member]
Dec. 31, 2013
Underwritten Offering [Member]
Aug. 31, 2013
Underwritten Offering [Member]
Oct. 31, 2012
Underwritten Offering [Member]
Mar. 31, 2012
Underwritten Offering [Member]
Feb. 28, 2010
Underwritten Offering [Member]
Dec. 18, 2013
Underwritten Offering [Member]
Aug. 23, 2013
Underwritten Offering [Member]
Oct. 29, 2012
Underwritten Offering [Member]
Mar. 09, 2012
Underwritten Offering [Member]
Registered Direct Offerings and Underwritten Offering [Abstract]                                  
Capital units issued (in shares)       695,652                 2,800,000 10,925,000 8,736,187 13,333,333 29,669,154
Common stock per capital unit (in shares)       1                 1       0.5
Common stock per capital unit called by stock warrant (in shares)       0.5                 0.45        
Gross proceeds from issuance of capital units       $ 12,000,000         $ 57,400,000 $ 31,600,000 $ 40,000,000 $ 39,200,000 $ 21,000,000        
Offering expense       800,000 1,000,000 100,000     3,800,000 2,200,000 3,000,000 3,000,000          
Purchase price of capital units (in dollars per share)       $ 17.25                   $ 5.25 $ 3.62 $ 3.00 $ 1.32
Number of shares called by warrants (in shares)       347,826                         14,834,577
Exercise price of warrants (in dollars per share)       $ 19.50                         $ 1.76
Period to purchase additional stock                 30 days 30 days 30 days            
Term of warrants                       5 years          
Warrant outstanding (in shares)                 12,562,682                
ATM Agreement [Abstract]                                  
Common stock sold (in shares)         7,560,862 821,386 7,572,327 0                  
Sales commission paid per transaction (in hundredths)             3.00%                    
Proceeds from issuance of common stock $ 84,338,000 $ 76,498,000 $ 15,143,000   $ 34,000,000 $ 4,400,000 $ 14,600,000 $ 500,000