Capital (Details) (USD $)
0 Months Ended 1 Months Ended 12 Months Ended
Aug. 25, 2011
Sep. 30, 2011
Dec. 31, 2013
Dec. 31, 2014
Capital        
Preferred stock, liquidation value (in dollars per share)     1,000.00 $ 1,000.00
Number of shares of common stock that can be purchased by exercise of warrants 1,147,666      
Percentage reduction in the number of shares of common stock that can be purchased by exercise of warrants 50.00%      
Number of shares of common stock that can be purchased by exercise of warrants, after reduction 573,833      
Warrants outstanding (in shares)     573,833  
Preferred stock, shares outstanding     72,664 72,664
Series C Preferred stock        
Capital        
Shares issued 72,664      
Preferred stock, liquidation value (in dollars per share) 1,000      
Aggregate proceeds from issuance of shares 72,664,000      
Series C Preferred stock | Initial dividend period        
Capital        
Dividend rate (as a percent)   5.00%    
Series C Preferred stock | Period from the 2nd through the 10th calendar quarters        
Capital        
Dividend rate (as a percent)     5.00%  
Series C Preferred stock | Period from the 11th calendar quarter through 4.5 years after issuance | Minimum        
Capital        
Dividend rate (as a percent)     1.00%  
Series C Preferred stock | Period from the 11th calendar quarter through 4.5 years after issuance | Maximum        
Capital        
Dividend rate (as a percent)     7.00%  
Series C Preferred stock | Period after 4.5 years from issuance        
Capital        
Dividend rate (as a percent)     9.00%  
Series T Preferred stock        
Capital        
Shares redeemed 100,000      
Redemption price 100,100,000