Quarterly report pursuant to Section 13 or 15(d)

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

v3.6.0.2
Fair Value Measurements - Schedule of financial assets and liabilities (Details) - USD ($)
Dec. 31, 2016
Sep. 30, 2016
Dec. 31, 2015
Sep. 30, 2015
Dec. 19, 2014
Financial assets and liabilities at carrying value and fair value          
Cash and cash equivalents $ 46,600,000 $ 52,000,000 $ 55,100,000 $ 48,300,000  
Level 1          
Assets:          
Cash and cash equivalents 46,600,000        
Investments in rabbi trust 4,200,000        
Derivative instruments 0        
Liabilities:          
Derivative instruments 0        
Level 2          
Assets:          
Cash and cash equivalents 0        
Investments in rabbi trust 0        
Derivative instruments 2,000,000        
Liabilities:          
Derivative instruments 5,400,000        
Level 3          
Assets:          
Cash and cash equivalents 0        
Investments in rabbi trust 0        
Derivative instruments 0        
Liabilities:          
Derivative instruments 0        
$150 senior unsecured notes          
Financial assets and liabilities at carrying value and fair value          
Debt instrument, face amount 150,000,000   150,000,000    
Assets:          
Long-term Debt, Gross 149,300,000        
$150 senior unsecured notes | Level 1          
Liabilities:          
Debt instruments 160,500,000        
$150 senior unsecured notes | Level 2          
Liabilities:          
Debt instruments 0        
$150 senior unsecured notes | Level 3          
Liabilities:          
Debt instruments 0        
Revolving credit facility          
Assets:          
Long-term Debt, Gross 245,700,000        
Revolving credit facility | Level 1          
Liabilities:          
Debt instruments 0        
Revolving credit facility | Level 2          
Liabilities:          
Debt instruments 245,700,000        
Revolving credit facility | Level 3          
Liabilities:          
Debt instruments 0        
Term loan          
Financial assets and liabilities at carrying value and fair value          
Debt instrument, face amount         $ 180,000,000.0
Assets:          
Long-term Debt, Gross 158,600,000        
Term loan | Level 1          
Liabilities:          
Debt instruments 0        
Term loan | Level 2          
Liabilities:          
Debt instruments 158,600,000        
Term loan | Level 3          
Liabilities:          
Debt instruments 0        
$100 Series A Notes          
Financial assets and liabilities at carrying value and fair value          
Debt instrument, face amount 100,000,000   $ 100,000,000    
Assets:          
Long-term Debt, Gross 100,000,000        
$100 Series A Notes | Level 1          
Liabilities:          
Debt instruments 0        
$100 Series A Notes | Level 2          
Liabilities:          
Debt instruments 104,900,000        
$100 Series A Notes | Level 3          
Liabilities:          
Debt instruments 0        
Derivatives | Cash flow hedging          
Financial assets and liabilities at carrying value and fair value          
Derivative, notional amount 202,700,000        
Reported Value Measurement          
Financial assets and liabilities at carrying value and fair value          
Cash and cash equivalents 46,600,000        
Assets:          
Investments in rabbi trust 4,200,000        
Derivative instruments 2,000,000        
Liabilities:          
Derivative instruments $ 5,400,000