Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Schedule of financial assets and liabilities (Details)

v3.10.0.1
Fair Value Measurements - Schedule of financial assets and liabilities (Details) - USD ($)
$ in Millions
Dec. 31, 2018
Sep. 30, 2018
Dec. 31, 2017
Financial assets and liabilities at carrying value and fair value      
Cash and cash equivalents $ 64.8 $ 56.0 $ 77.8
Level 1      
Assets:      
Cash and cash equivalents 64.8    
Investments in rabbi trust 4.6    
Derivative instruments 0.0    
Liabilities:      
Derivative instruments 0.0    
Level 2      
Assets:      
Cash and cash equivalents 0.0    
Investments in rabbi trust 0.0    
Derivative instruments 1.5    
Liabilities:      
Derivative instruments 7.5    
Level 3      
Assets:      
Cash and cash equivalents 0.0    
Investments in rabbi trust 0.0    
Derivative instruments 0.0    
Liabilities:      
Derivative instruments 0.0    
$150 senior unsecured notes      
Assets:      
Long-term Debt, Gross 149.7    
$150 senior unsecured notes | Level 1      
Liabilities:      
Debt instruments 153.6    
$150 senior unsecured notes | Level 2      
Liabilities:      
Debt instruments 0.0    
$150 senior unsecured notes | Level 3      
Liabilities:      
Debt instruments 0.0    
Revolving credit facility      
Assets:      
Long-term Debt, Gross 115.8    
Revolving credit facility | Level 1      
Liabilities:      
Debt instruments 0.0    
Revolving credit facility | Level 2      
Liabilities:      
Debt instruments 115.8    
Revolving credit facility | Level 3      
Liabilities:      
Debt instruments 0.0    
$100 Series A Notes      
Assets:      
Long-term Debt, Gross 100.0    
$100 Series A Notes | Level 1      
Liabilities:      
Debt instruments 0.0    
$100 Series A Notes | Level 2      
Liabilities:      
Debt instruments 100.8    
$100 Series A Notes | Level 3      
Liabilities:      
Debt instruments 0.0    
Derivatives | Cash flow hedging      
Financial assets and liabilities at carrying value and fair value      
Derivative, notional amount 283.1    
Reported Value Measurement      
Assets:      
Investments in rabbi trust 4.6    
Derivative instruments 1.5    
Liabilities:      
Derivative instruments $ 7.5