Quarterly report pursuant to Section 13 or 15(d)

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

v3.5.0.2
Fair Value Measurements - Schedule of financial assets and liabilities (Details) - USD ($)
Jun. 30, 2016
Sep. 30, 2015
Jun. 30, 2015
Dec. 31, 2014
Dec. 19, 2014
Dec. 15, 2014
Sep. 30, 2014
Financial assets and liabilities at carrying value and fair value              
Cash and cash equivalents $ 47,600,000 $ 48,300,000 $ 45,600,000       $ 58,000,000
Assets:              
Long-term Debt 637,000,000 528,100,000          
Level 1              
Assets:              
Cash and cash equivalents 47,600,000            
Investments in rabbi trust 3,800,000            
Derivative instruments 0            
Liabilities:              
Derivative instruments 0            
Level 2              
Assets:              
Cash and cash equivalents 0            
Investments in rabbi trust 0            
Derivative instruments 3,500,000            
Liabilities:              
Derivative instruments 6,300,000            
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 149,200,000 149,100,000          
$150 senior unsecured notes | Level 1              
Liabilities:              
Debt instruments 165,000,000            
$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 223,500,000 107,600,000          
Revolving credit facility | Level 1              
Liabilities:              
Debt instruments 0            
Revolving credit facility | Level 2              
Liabilities:              
Debt instruments 223,500,000            
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         $ 180.0    
Assets:              
Long-term Debt 164,300,000 171,000,000          
Term loan | Level 1              
Liabilities:              
Debt instruments 0            
Term loan | Level 2              
Liabilities:              
Debt instruments 164,300,000            
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   $ 100.0  
Assets:              
Long-term Debt 100,000,000 $ 100,000,000          
$100 Series A Notes | Level 1              
Liabilities:              
Debt instruments 0            
$100 Series A Notes | Level 2              
Liabilities:              
Debt instruments 108,200,000            
$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 215,100,000            
Reported Value Measurement [Member]              
Assets:              
Investments in rabbi trust 3,800,000            
Derivative instruments 3,500,000            
Liabilities:              
Derivative instruments $ 6,300,000