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Stock Compensation Plans (Purchased Restricted Stock Plan) (Narrative) (Details) (PRS [Member], USD $)
In Millions, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
PRS [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of discount on fair market value on grant date 50.00%    
Number of shares issued 174,212 213,714 218,134
Value of shares purchased by employees $ 5.4 $ 4.8 $ 3.0
Shares purchased by employees 87,106 106,857 109,067
Total fair value of vested 7.9    
Unrecognized compensation cost related to non-vested stock options and SSAR, RSU, PRS and Cash RSU awards granted $ 4.3    
Unrecognized compensation cost related to non-vested stock options and SSAR, RSU, PRS and Cash RSU awards granted, weighted average period, in years 1.8