INCOME TAXES - COMPONENTS OF INCOME TAX PROVISION (BENEFIT) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Current:
Federal	$ (2,164)	$ 10,933	$ (2,848)
State	6,763	3,530	4,563
Deferred:
Federal	31,577	7,988	(40,785)
State	(900)	5,833	6,731
Investment/production tax credits	(42,220)	(66,035)	(21,446)
Income tax benefit	$ (6,944)	$ (37,751)	$ (53,785)