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Stock-based Compensation Plans (Narrative) (Details)
$ / shares in Units, $ in Millions
3 Months Ended
Dec. 31, 2017
USD ($)
$ / shares
shares
Dec. 31, 2016
USD ($)
shares
Allocated Share-based Compensation Expense | $ $ 2.4 $ 2.7
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized | $ $ 8.9  
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 70,996 323,010
Phantom Share Units (PSUs) [Member]    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Intrinsic Value, Amount Per Share | $ / shares $ 12.53  
Share-based compensation liability | $ $ 1.2  
Performance Shares [Member]    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period 146,061 263,410
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period 171,288  
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period   3 years
Share-based compensation, units awarded but not yet granted 185,270  
Restricted Stock Units (RSUs) [Member]    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period 213,532  
Minimum [Member] | Performance Shares [Member]    
Performance Factor   0
Maximum [Member] | Performance Shares [Member]    
Performance Factor   2