Fair Value of Financial Instruments - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Sep. 30, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term debt, carrying value	$ 1,374,780		$ 1,374,780		$ 1,678,268
Credit valuation adjustment to total fair value percentage (less than)	1.00%		1.00%
Allowance for doubtful accounts	$ 2,400		$ 2,400		3,800
Provision for doubtful accounts	3,400	$ 200	4,500	$ 300
Senior Notes | 6.5% Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term debt, carrying value	489,780		489,780		$ 648,268
Principal amount	490,700		490,700
Long-term Debt, Fair Value	$ 367,000		$ 367,000