Fair Value Measurements - Carrying Values and Estimated Fair Values of Other Financial Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior Notes	$ 1,435,183	$ 1,416,860
Junior Subordinated Notes	55,736	53,670
Long-term Debt, Fair Value	1,490,919	1,470,530
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior Notes	1,462,899	1,469,904
Junior Subordinated Notes	55,736	53,670
Long-term Debt, Fair Value	$ 1,518,635	$ 1,523,574