Fair Value Measurements - Carrying Values and Estimated Fair Values of Other Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Sep. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total debt, net	$ 1,528,275	$ 1,535,433
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior Notes	1,427,240	1,435,183
Junior Subordinated Notes	57,803	55,736
Total debt, net	1,485,043	1,490,919
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior Notes	1,412,173	1,462,899
Junior Subordinated Notes	57,803	55,736
Total debt, net	$ 1,469,976	$ 1,518,635