GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION - Debt (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Mar. 19, 2015
Financial Information
Percentage ownership of subsidiary	100.00%
Debt issued	$ 500,000	$ 500,000
Unsecured senior notes issued March 19, 2015
Financial Information
Debt issued	500,000	$ 500,000	$ 500,000
Issuer Subsidiary | Unsecured senior notes issued March 19, 2015
Financial Information
Debt issued	$ 500,000