Annual report pursuant to Section 13 and 15(d)

Stock-based compensation (Details)

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Stock-based compensation (Details) (USD $)
 12 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2010
Stock-Based Compensation      
Shares available for grants (in shares) 1,647,669,000,000    
Information pertaining to stock options vested and exercised      
Total income tax benefit recognized $ 4,300,000 $ 3,700,000 $ 3,100,000
RSUs
      
Stock-Based Compensation      
Compensation expense recognized 12,100,000 9,400,000 7,100,000
Summary of RSU activity      
Non-vested shares outstanding at the beginning of the period (in shares) 1,527,686    
Granted (in shares) 414,894    
Vested (in shares) (452,804)    
Forfeited (in shares) (43,706)    
Non-vested shares outstanding at the end of the period (in shares) 1,446,070 1,527,686  
Weighted-Average Grant-Date Fair value      
Non-vested shares outstanding at the beginning of the period (in dollars per share) $ 22.64    
Granted (in dollars per share) $ 42.01 $ 31.80 $ 23.58
Vested (in dollars per share) $ 24.32    
Forfeited (in dollars per share) $ 21.35    
Non-vested shares outstanding at the end of the period (in dollars per share) $ 27.71 $ 22.64  
Total fair value 25,000,000 14,500,000 9,900,000
Total unrecognized compensation cost related to unvested RSUs 28,100,000    
Unrecognized compensation cost period expected to be realize 4 years    
Weighted Average Disclosure      
Weighted average remaining life 1 year 7 months 6 days    
Information pertaining to stock options vested and exercised      
Cash paid to satisfy employees personal tax liability 4,500,000 3,500,000 3,200,000
RSUs awarded before 2009
      
Stock-Based Compensation      
Award vesting period 6 years    
RSUs awarded in 2009 and after
      
Stock-Based Compensation      
Award vesting period 5 years    
Stock options
      
Stock-Based Compensation      
Award vesting period 4 years    
Compensation expense recognized   100,000 800,000
Summary of stock option activity      
Outstanding at the beginning of the period (in shares) 765,676    
Exercised (in shares) (404,563)    
Forfeited or expired (in shares) (934)    
Outstanding at the end of the period (in shares) 360,179 765,676  
Weighted Average Disclosure      
Outstanding at the beginning of the period (in dollars per share) $ 16.18    
Exercised (in dollars per share) $ 15.92    
Forfeited or expired (in dollars per share) $ 15.37    
Outstanding at the end of the period (in dollars per share) $ 16.52 $ 16.18  
Intrinsic value of outstanding and exercisable stock options at the end of the period 15,600,000    
Weighted average remaining life 2 years 6 months    
Information pertaining to stock options vested and exercised      
Aggregate intrinsic value of all stock options exercised 10,920,000 15,102,000 4,730,000
Net cash proceeds from exercise of stock options 6,441,000 12,482,000 5,948,000
Stock options | Maximum
      
Stock-Based Compensation      
Compensation expense recognized $ 100,000    
Stock options issued prior to fiscal 2005
      
Stock-Based Compensation      
Award vesting period 10 years    
Stock options issued in fiscal 2005 and after
      
Stock-Based Compensation      
Award vesting period 6 years