Quarterly report pursuant to Section 13 or 15(d)

Equity - Based Compensation (Details)

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Equity - Based Compensation (Details) (USD $)
In Millions, except Share data, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Dec. 31, 2011
Long Term Incentive Plans (Textual) [Abstract]          
Aggregate number of shares of common stock that may be issued for awards pursuant to the 2011 plan 11,750,000   11,750,000    
Aggregate number of shares of common stock that may be issued pursuant to the terms of the 2007 Plan     4,000,000    
Restricted Stock [Member]
         
Additional Long Term Incentive Plans (Textual) [Abstract]          
Granted, shares 89,293 67,198 1,300,000 900,000  
Granted, per share $ 22.17 $ 19.90 $ 21.69 $ 22.16  
Vested, shares 52,950 55,128 900,000 900,000  
Fair value of restricted stock, vested $ 1.2 $ 1.1 $ 19.7 $ 20.0  
Unrecognized compensation cost, related to unvested restricted stock, total 34.6   34.6    
Expected weighted average period to recognized compensation cost on restricted stock (in years)     2 years 1 month 2 days    
Vesting period for restricted stock and restricted stock units     3 years 3 years  
Restricted Stock Units (RSUs) [Member]
         
Additional Long Term Incentive Plans (Textual) [Abstract]          
Vesting period for restricted stock and restricted stock units     3 years    
Compensation expense related to Restricted Stock Units 0.5 0.2 0.8 0.5  
Payment to settle liabilities under compensation plan 0.3 0.1 0.3 0.1  
Liabilities under Compensation Plan $ 1.1   $ 1.1   $ 1.3