Fair Value Measurements - Carrying Values and Estimated Fair Values of Other Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Sep. 30, 2015
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying values and estimated fair values of other financial assets and liabilities	$ 1,443,133	$ 1,485,043
Carrying Amount | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior Notes	1,246,309	1,427,240
Carrying Amount | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Term Loan, Net	137,987	0
Junior Subordinated Notes	58,837	57,803
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying values and estimated fair values of other financial assets and liabilities	1,327,781	1,469,976
Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior Notes	1,130,957	1,412,173
Fair Value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Term Loan, Net	137,987	0
Junior Subordinated Notes	$ 58,837	$ 57,803