v2.4.0.6
Summary of Significant Accounting Policies (Details 2) (USD $)
 3 Months Ended 12 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Dec. 31, 2010
Dec. 31, 2011
Earnings Per Share        
Preferred stock, shares outstanding 12,275     12,275
Net income loss available to common stockholders        
Net income $ 78,619,000 $ 51,528,000    
Net income applicable to preferred stock 15,272,000 9,785,000    
Net income 63,347,000 41,743,000    
Determination of shares:        
Weighted-average common shares outstanding (in shares) 75,994,000 78,162,000    
Assumed conversion of dilutive employee stock-based awards (in shares) 2,360,000 1,479,000    
Assumed conversion of preferred stock (in shares) 27,278,000 27,278,000    
Diluted weighted-average common shares outstanding (in shares) 105,632,000 106,919,000    
Repurchase of Preferred Stock (in shares)     225  
Anti-dilutive securities, options to purchase shares outstanding 3,122,903 3,734,446    
Calculation of basic EPS:        
Net income applicable to common stock 63,347,000 41,743,000    
Weighted-average common shares outstanding (in shares) 75,994,000 78,162,000    
Basic earnings per common share $ 0.83 $ 0.53    
Calculation of diluted EPS:        
Net income 78,619,000 51,528,000    
Diluted weighted-average common shares outstanding 105,632,000 106,919,000    
Diluted earnings per common share $ 0.74 $ 0.48    
Common stock price less than $45
        
Determination of shares:        
Common stock price (in dollars per share) $ 45      
Increase in diluted weighted-average common shares outstanding 27,277,778      
Common stock price between $45 and $67
        
Determination of shares:        
Aggregate liquidation preference of preferred stock $ 1,230,000,000      
Common stock price between $45 and $67 | Maximum
        
Determination of shares:        
Common stock price (in dollars per share) $ 67      
Increase in diluted weighted-average common shares outstanding 27,277,778      
Common stock price between $45 and $67 | Minimum
        
Determination of shares:        
Common stock price (in dollars per share) $ 45      
Increase in diluted weighted-average common shares outstanding 18,320,896      
Common stock price more than $67
        
Determination of shares:        
Common stock price (in dollars per share) $ 67      
Increase in diluted weighted-average common shares outstanding 18,320,896