Fair Value Measurements - Schedule of financial assets and liabilities (Details) - USD ($)	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014	Dec. 19, 2014	Sep. 30, 2014
Financial assets and liabilities at carrying value and fair value
Cash and cash equivalents	$ 55,100,000	$ 48,300,000	$ 52,000,000		$ 58,000,000
Assets:
Long-term Debt	623,000,000	528,100,000
Level 1
Assets:
Cash and cash equivalents	55,100,000
Investments in rabbi trust	4,400,000
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	6,400,000
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		149,100,000
$150 senior unsecured notes | Level 1
Liabilities:
Debt instruments	162,300,000
$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		107,600,000
Revolving credit facility | Level 1
Liabilities:
Debt instruments	0
Revolving credit facility | Level 2
Liabilities:
Debt instruments	205,100,000
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		171,000,000
Term loan | Level 1
Liabilities:
Debt instruments	0
Term loan | Level 2
Liabilities:
Debt instruments	168,800,000
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		$ 100,000,000
$100 Series A Notes | Level 1
Liabilities:
Debt instruments	0
$100 Series A Notes | Level 2
Liabilities:
Debt instruments	99,400,000
$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	177,900,000
Carrying value
Financial assets and liabilities at carrying value and fair value
Cash and cash equivalents	55,100,000
Assets:
Investments in rabbi trust	4,400,000
Derivative instruments	2,000,000
Liabilities:
Derivative instruments	6,400,000
Carrying value | $150 senior unsecured notes
Assets:
Long-term Debt	149,100,000
Carrying value | Revolving credit facility
Assets:
Long-term Debt	205,100,000
Carrying value | Term loan
Assets:
Long-term Debt	168,800,000
Carrying value | $100 Series A Notes
Assets:
Long-term Debt	$ 100,000,000