Fair Value of Financial Instruments - Narrative (Details) - USD ($)	Dec. 31, 2015	Sep. 30, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term debt, carrying value	$ 1,608,399,000	$ 1,678,268,000
Credit valuation adjustment to total fair value percentage (less than)	1.00%
Senior Notes | 6.5% Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term debt, carrying value	$ 648,399,000	$ 648,268,000
Principal amount	650,000,000
Long-term debt, fair value	$ 359,000,000