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Stock Based Compensation Option Rollforward (Details) (Common Shares, 2005 Long-Term Incentive Plan, Stock Options, USD $)
 12 Months Ended
Dec. 31, 2011
Year
Dec. 31, 2010
Dec. 31, 2009
Common Shares | 2005 Long-Term Incentive Plan | Stock Options
      
Stock compensation, stock option rollforward schedule, number of shares      
Outstanding, begin of period 2,262,000 2,029,000 1,626,000
Exercisable options, begin of period 1,151,000 1,046,000 624,000
Granted options 595,000 831,000 748,000
Exercised options (173,000) (317,000) (181,000)
Forfeited options (72,000) (88,000) (130,000)
Expired options (175,000) (193,000) (34,000)
Outstanding, end of period 2,437,000 2,262,000 2,029,000
Exercisable options, end of period 1,321,000 1,151,000 1,046,000
Stock compensation, stock option rollforward schedule, other information      
Options outstanding, begin of period - weighted average exercise price $ 49.12 $ 51.37 $ 57.15
Options exercisable, begin of period - weighted average exercise price $ 54.64 $ 54.40 $ 51.56
Options granted, weighted average exercise price $ 51.70 $ 41.98 $ 34.21
Options exercised, weighted average exercise price $ 37.50 $ 38.60 $ 34.01
Options forfeited, weighted average exercise price $ 45.97 $ 44.28 $ 47.98
Options expired, weighted average exercise price $ 57.05 $ 61.50 $ 56.84
Options outstanding, end of period - weighted average exercise price $ 50.10 $ 49.12 $ 51.37
Options exercisable, end of period - weighted average exercise price $ 53.68 $ 54.64 $ 54.40
Options granted, weighted average grant date fair value $ 19.42 $ 13.75 $ 11.75
Aggregate intrinsic value, options exercised $ 2,099,000 $ 1,555,000 $ 821,000
Aggregate intrinsic value, options outstanding 4,423,000    
Aggregate intrinsic value, options exercisable $ 2,361,000    
Weighted average remaining contractual life, outstanding 6.9    
Weighted average remaining contractual life, exercisable 5.5