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Stock-Based Compensation - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based payment award, award vesting period     3 years  
Share-based compensation expense $ 1.4 $ 0.9 $ 5.0 $ 2.7
Tax benefit from compensation expense 0.5 $ 0.3 $ 1.9 $ 1.0
Target performance level (as a percent)     100.00%  
Share-based compensation, compensation cost not yet recognized $ 6.3   $ 6.3  
Share-based compensation, compensation cost not yet recognized, recognition period     2 years 5 months 1 day  
Minimum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Pre-established target levels (as a percent)     0.00%  
Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Target performance level (as a percent)     150.00%  
Pre-established target levels (as a percent)     150.00%  
Performance shares        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Approximate number of shares to be issued (in shares)     407,867  
Restricted shares        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Fair value of vested stock awards     $ 1.2