Fair Value Measurements - Schedule of Other Fair Value Disclosures (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Sep. 30, 2017
Carrying Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt	$ 1,860,265	$ 1,891,480
Carrying Value | Senior Notes | Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt	950,000	950,000
Carrying Value | Other Long-Term Debt | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt	910,265	941,480
Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt	1,784,039	1,919,930
Fair Value | Senior Notes | Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt	889,115	973,750
Fair Value | Other Long-Term Debt | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt	$ 894,924	$ 946,180