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Incentive Plans - Additional Information (Detail) (USD $)
1 Months Ended9 Months Ended12 Months Ended1 Months Ended
Feb. 28, 2011
Sep. 30, 2011
Sep. 30, 2010
Dec. 31, 2007
Annual Incentive Plan, 2007 Annual Plan
Dec. 31, 2007
Employee Stock Purchase Plan
Feb. 28, 2011
Stock Options
Feb. 28, 2011
Minimum
Performance-Based Restricted Stock
Feb. 28, 2011
Performance-Based Restricted Stock
Feb. 28, 2011
Performance-Based Restricted Stock
Maximum
Aug. 31, 2011
Time-Lapse Restricted Stock
Feb. 28, 2011
Time-Lapse Restricted Stock
Compensation Related Costs Share Based Payments Disclosure [Line Items]           
Maximum number of shares available for issuance   6,700,000980,000      
Maximum number of shares available for issuance, annual Rate   1.00%       
Granted stock options1,397,312          
Granted stock options, exercise price$ 67.635          
Granted stock options, valuation per option$ 20.34          
Granted restricted stock       521,423 3,59629,115
Granted restricted stock, valuation      $ 38.94 $ 64.89$ 60.41$ 67.64
Stock award, valuation method     Black-Scholes valuation model Monte Carlo valuation model   
Employee Stock purchase plan, vesting scheme          These shares vest on the third anniversary of the date of grant.
Proceeds from exercise of stock options and employee stock purchase plans $ 8,245,000$ 26,100,000[1]        
Income tax benefit realized for the tax deductions from option exercises $ 7,400,000$ 11,700,000        
[1]Reclassified to conform to current presentation