Fair Value Measurements - Carrying Values and Estimated Fair Values of Other Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Sep. 30, 2015
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior Notes	$ 1,207,526	$ 1,415,332
Term Loan	52,669	0
Junior Subordinated Notes	59,870	57,803
Total debt, net	1,320,065	1,473,135
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior Notes	1,253,614	1,412,173
Term Loan	52,669	0
Junior Subordinated Notes	59,870	57,803
Total debt, net	$ 1,366,153	$ 1,469,976