INCOME TAXES - Effective tax rate (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Effective income tax rates as compared to the U.S. Federal income tax rate
Income tax (benefit) provision	$ 25,078	$ (3,922)	$ 26,429	$ (504,563)
Effective income tax rate (as a percent)	25.90%	70.60%	24.80%	9084.70%
Tax Cuts and Jobs Act of 2017, remeasurement of deferred taxes				$ 506,400