Annual report pursuant to Section 13 and 15(d)

Share-Based Compensation (Details)

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Share-Based Compensation (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2014
Compensation Related Costs [Abstract]      
Number of shares initially registered and authorized for issuance 12,685,436    
Total number of shares outstanding (in shares) 3,504,376    
Number of shares issued (in shares) 4,759,805    
Number of shares available for future issuance (in shares) 4,421,255    
Stock-based compensation cost $ 8.5 $ 12.0 $ 7.5
Less impact of income tax 3.1 4.4 2.8
Stock-based compensation cost, net of tax 5.4 $ 7.6 $ 4.7
Current tax benefit realized from the exercise of stock options and payment of restricted stock units 5.6    
Time Based Stock Awards      
Weighted average exercise price      
Unrecognized stock-based compensation $ 1.1    
Period for recognition of unrecognized stock-based compensation 1 year 7 months 9 days    
Number of shares      
Number of shares outstanding under time-based stock awards and performance-based stock awards at the beginning of the period (in shares) 81,443    
Granted (in shares) 43,824    
Vested (in shares) (40,089)    
Forfeited (in shares) (2,563)    
Number of shares outstanding under time-based stock awards and performance-based stock awards at the end of the period (in shares) 82,615 81,443  
Weighted-Average Grant Date Fair Value      
Non-vested time-based stock awards at the beginning of the period (in dollars per share) $ 27.56    
Granted (in dollars per share) 30.59 $ 30.99 $ 29.50
Vested (in dollars per share) 23.36    
Forfeited (in dollars per share) 31.11    
Non-vested time-based stock awards at the end of the period (in dollars per share) $ 30.80 $ 27.56  
Aggregate fair value $ 2.7    
Time Based Stock Awards and Performance Based Stock Awards      
Time-based stock awards and performance-based stock awards      
Total vest date fair value of vested time-based stock awards and performance-based stock awards shares held by employees and directors $ 7.4 $ 7.1 $ 5.8
Weighted-Average Grant Date Fair Value      
Number of shares under the time-based and performance-based stock awards due to dividend reinvestment (in shares) 25,892    
Aggregate fair value of shares under the time-based and performance-based stock awards plans due to dividend reinvestment $ 0.8    
Vested Deferred Stock      
Vested deferred stock (in shares) 337,837    
Aggregate fair value of vested deferred stock $ 10.7    
Employee Stock Option      
Share-based compensation      
Vesting period 3 years    
Weighted average fair value of options granted (in dollars per share) $ 7.80 $ 8.38 $ 6.97
Assumptions used in the determination of fair value of options      
Weighted-average dividend yield (as a percent) 2.60% 2.50% 2.80%
Weighted-average volatility factor (as a percent) 31.00% 31.80% 33.50%
Exercise factor (as a percent) 33.60% 33.10% 29.50%
Post-vesting termination rate (as a percent) 5.00% 5.00% 5.00%
Expected life 4 years 6 months 1 day 4 years 7 months 6 days 4 years 2 months 12 days
Number of shares      
Outstanding at the beginning of the period (in shares) 2,517,132    
Granted (in shares) 497,774    
Exercised (in shares) (670,216)    
Forfeited (in shares) (64,378)    
Expired (in shares) (5,716)    
Outstanding at the end of the period (in shares) 2,274,596 2,517,132  
Exercisable at the end of the period (in shares) 1,529,560    
Weighted average exercise price      
Outstanding at the beginning of the period (in dollars per share) $ 22.95    
Granted (in dollars per share) 31.11    
Exercised (in dollars per share) 19.82    
Forfeited (in dollars per share) 31.07    
Expired (in dollars per share) 26.35    
Outstanding at the end of the period (in dollars per share) 25.41 $ 22.95  
Exercisable at the end of the period (in dollars per share) $ 22.63    
Unrecognized stock-based compensation $ 2.7    
Period for recognition of unrecognized stock-based compensation 1 year 9 months 13 days    
Average remaining life of outstanding stock options 6 years    
Aggregate intrinsic value of outstanding options $ 14.5    
Average remaining life of the exercisable options 4 years 8 months 16 days    
Aggregate intrinsic value of exercisable options $ 13.9    
Total intrinsic value of options exercised $ 7.5 $ 2.8 $ 6.1
Employee Stock Option | Minimum      
Assumptions used in the determination of fair value of options      
Risk-free interest rate (as a percent) 0.50% 0.10% 0.10%
Employee Stock Option | Maximum      
Share-based compensation      
Award expiration term 10 years    
Assumptions used in the determination of fair value of options      
Risk-free interest rate (as a percent) 2.20% 2.20% 2.80%
Performance Shares      
Weighted average exercise price      
Unrecognized stock-based compensation $ 5.5    
Period for recognition of unrecognized stock-based compensation 1 year 6 months 15 days    
Time-based stock awards and performance-based stock awards      
Performance measurement period used to determined shares granted included in performance-based stock awards 3 years    
Number of shares      
Number of shares outstanding under time-based stock awards and performance-based stock awards at the beginning of the period (in shares) 936,051    
Granted (in shares) 378,158    
Vested (in shares) (146,757)    
Forfeited (in shares) (384,016)    
Number of shares outstanding under time-based stock awards and performance-based stock awards at the end of the period (in shares) 783,436 936,051  
Weighted-Average Grant Date Fair Value      
Non-vested time-based stock awards at the beginning of the period (in dollars per share) $ 30.91    
Granted (in dollars per share) 33.14 $ 33.44 $ 28.56
Vested (in dollars per share) 28.71    
Forfeited (in dollars per share) 29.00    
Non-vested time-based stock awards at the end of the period (in dollars per share) $ 33.33 $ 30.91  
Aggregate fair value $ 23.8