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Stock Plans (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
Jun. 30, 2012
Restricted Stock Awards for Certain Management [Member]
Jun. 30, 2012
Restricted Stock Awards for Certain Management [Member]
Maximum [Member]
Jun. 30, 2012
Restricted Stock Awards for Certain Management [Member]
Minimum [Member]
Jun. 30, 2012
Equity Incentive Plan Restricted Stock [Member]
Dec. 31, 2011
Equity Incentive Plan Restricted Stock [Member]
Stock Plans (Textual) [Abstract]                  
Weighted-average grant-date fair value of restricted stock awards granted         $ 39.88     $ 30.23  
Restricted stock award, outstanding               861,317 633,647
Restricted stock award granted by Company         104,500     311,230  
Possible vesting date         2015        
Volatility of weighted-average grant date fair value           238.00% 15.00%    
Risk-free rate of weighted-average grant date fair value         0.54%        
Expected life assumption for weighted average grant date fair value         3 years        
Additional Stock Plans (Textual) [Abstract]                  
Compensation cost on stock-based compensation plans $ 2.9 $ 2.5 $ 5.3 $ 4.8