Debt - Credit Facility (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				3 Months Ended
	Dec. 31, 2012	Dec. 31, 2012 Senior Notes Due May 2021 [Member]	Sep. 30, 2012 Senior Notes Due May 2021 [Member]	Dec. 31, 2012 Senior Notes Due May 2022 [Member]	Dec. 31, 2012 Private Placement Notes [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum					4.30%
Line of Credit Facility, Maximum Borrowing Capacity	$ 450
Line of Credit Facility, Amount Outstanding	65.0
Line of Credit Facility, Remaining Borrowing Capacity	373.9
Letters of Credit Outstanding, Amount	$ 11.1
Line of Credit Facility, Maximum Debt to EBITDA Ratio Allowed	4.0
Line of Credit Facility, Debt to EBITDA Ratio, Threshold for Four Consecutive Quarters	3.5
Line of Credit Facility, Additional Basis Points When Debt to EBITDA Ratio is Above Threshold	0.75%
Line of Credit Facility, Minimum EBIT to Interest Expense Ratio Allowed	3.0
Line of Credit Facility, Actual Debt to EBITDA Ratio	2.6
Line of Credit Facility, Actual EBIT to Interest Expense Ratio	5.6
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum					6.60%
Debt Instrument, Interest Rate, Stated Percentage		4.70%	4.70%	4.70%