Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Jul. 09, 2010
$150 senior unsecured notes
Financial assets and liabilities at carrying value and fair value
Long-term debt, principal	$ 150	$ 150	$ 150
Liabilities:
Stated interest rate (as a percent)	5.50%
Term of debt issued	10 years
Carrying Value
Assets:
Cash and cash equivalents	20.2	115.5
Equity investments	2.5	3.6
Investments in rabbi trust	5.5	5.2
Derivative instruments		0.4
Carrying amount of private equity limited partnerships for which fair value is not readily available	13.3	13.8
Liabilities:
Revolving credit facility	123.0	283.0
$150 senior unsecured notes	148.6	148.5
Derivative instruments	0.4
Level 1
Assets:
Cash and cash equivalents	20.2	115.5
Equity investments	1.5	2.6
Investments in rabbi trust	5.5	5.2
Liabilities:
$150 senior unsecured notes	165.6	157.6
Level 2
Assets:
Derivative instruments		0.4
Liabilities:
Revolving credit facility	123.0	277.9
Derivative instruments	0.4
Level 3
Assets:
Equity investments	$ 1.0	$ 1.0