SHAREHOLDERS' EQUITY - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
After-tax amounts:
Accumulated other comprehensive income (loss)	$ (25,274)	$ (26,188)
Unrecognized net actuarial loss
Pre-tax amounts:
Accumulated other comprehensive income (loss)	(32,743)	(33,923)
After-tax amounts:
Accumulated other comprehensive income (loss)	(25,274)	(26,188)
Accumulated Other Comprehensive Income (Loss)
Pre-tax amounts:
Accumulated other comprehensive income (loss)	(32,743)	(33,923)
After-tax amounts:
Accumulated other comprehensive income (loss)	$ (25,274)	$ (26,188)