Quarterly report pursuant to Section 13 or 15(d)

Financing Agreements - Schedule of borrowings (Details)

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Financing Agreements - Schedule of borrowings (Details)
$ in Millions
3 Months Ended 6 Months Ended 12 Months Ended
Mar. 31, 2019
USD ($)
Mar. 31, 2018
Mar. 31, 2019
USD ($)
Mar. 31, 2018
Sep. 30, 2018
USD ($)
Dec. 15, 2014
Debt Instrument [Line Items]            
Total debt $ 363.4   $ 363.4   $ 344.6  
Other Long-term Debt, Current 1.7   1.7   0.0  
Long-term debt $ 361.7   $ 361.7   $ 344.6  
Debt Instrument, Covenant Holiday, Maximum Ratio of Indebtedness to Earnings before Interest, Taxes, Depreciation, and Amortization         3.5  
$900 revolving credit facility (excluding outstanding letters of credit)            
Debt Instrument [Line Items]            
Debt Instrument, Interest Rate During Period 2.73% 2.03% 2.57% 1.82%    
Total debt $ 112.6   $ 112.6   $ 95.7  
$150 senior unsecured notes, net of discount (1)            
Debt Instrument [Line Items]            
Total debt 149.5   149.5   149.3  
$100 Series A Notes (2)            
Debt Instrument [Line Items]            
Total debt $ 99.6   $ 99.6   $ 99.6  
Stated interest rate           4.60%