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Employee Benefit Plans (Details) - November Two Thousand Eighteen Grant [Member]
$ / shares in Units, $ in Millions
1 Months Ended 3 Months Ended 6 Months Ended
Nov. 30, 2018
$ / shares
shares
Mar. 31, 2019
USD ($)
Mar. 31, 2019
USD ($)
grant_recipient
$ / shares
shares
Performance Shares [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
RSUs granted in the period | shares 360,000    
Award vesting period 3 years    
Fair value of equity awards on the date of grant (in US$ per unit) | $ / shares $ 37.75    
Compensation expense   $ 1.4 $ 3.1
Performance Shares [Member] | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of total units granted that vest in the period 10.00%    
Performance Shares [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of total units granted that vest in the period 200.00%    
Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
RSUs granted in the period | shares     1,800,000
Fair value of equity awards on the date of grant (in US$ per unit) | $ / shares     $ 33.75
Compensation expense   $ 3.0 $ 7.4
RSU Grant Recipients | grant_recipient     900
Restricted Stock Units (RSUs) [Member] | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period     3 years
Restricted Stock Units (RSUs) [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period     5 years
Retirement Eligible [Member] | Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense     $ 3.5