Fair Value - Narrative (Details) (USD $)	Mar. 31, 2014	Sep. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term debt, carrying value	$ 1,512,685,000	$ 1,263,232,000
Senior Notes | 6.5% Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Stated interest rate	6.50%	6.50%
Long-term debt, carrying value	657,685,000	658,232,000
Principal amount	650,000,000
Long-term debt, fair value	$ 702,000,000
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Credit valuation adjustment to total fair value percentage (less than 1%)	1.00%