INCOME TAXES (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Operating Loss Carryforwards [Line Items]
Deferred employer portion of OASDI	$ 5,100		$ 3,100
Forecasted effective tax rate	19.90%	19.40%
Revaluation of deferred tax assets and liabilities	$ (145)	$ 2,700
Actual effective tax rate	19.70%	18.00%
Deferred tax assets, operating loss carryforwards, domestic, refundable and receivables	$ 22,800		22,800
Deferred tax assets, operating loss carryforwards, domestic	24,100
ITC carryforward	$ 193,200		195,200
Effective term	20 years
Valuation allowance	$ 17,600		17,600
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	134,000		134,000
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 442,400		$ 487,700
State | Minimum
Operating Loss Carryforwards [Line Items]
Effective term	7 years
State | Maximum
Operating Loss Carryforwards [Line Items]
Effective term	20 years