SHAREHOLDERS' EQUITY - Summary of Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2023	Mar. 31, 2022	Sep. 30, 2022
Components of accumulated other comprehensive income (loss)
Accumulated other comprehensive loss	$ (11,560)				$ (11,560)		$ (12,072)
Rollforward of accumulated other comprehensive income (loss), net of tax
Beginning balance	2,745,145	$ 2,765,472	$ 2,776,591	$ 2,912,618	2,765,472	$ 2,912,618
Other comprehensive income	256	256	394	394	512	788
Ending balance	2,755,806	2,745,145	2,734,410	2,776,591	2,755,806	2,734,410
Unrealized actuarial loss
Components of accumulated other comprehensive income (loss)
Unrealized actuarial loss	(15,041)				(15,041)		(15,703)
Accumulated other comprehensive loss	(11,560)				(11,560)		(12,072)
Rollforward of accumulated other comprehensive income (loss), net of tax
Beginning balance	(11,816)	(12,072)			(12,072)
Amounts reclassified from accumulated other comprehensive loss	256				512
Other comprehensive income	256				512
Ending balance	(11,560)	(11,816)			(11,560)
Accumulated Other Comprehensive Income (Loss)
Components of accumulated other comprehensive income (loss)
Unrealized actuarial loss	(15,041)				(15,041)		(15,703)
Accumulated other comprehensive loss	(11,560)				(11,560)		$ (12,072)
Rollforward of accumulated other comprehensive income (loss), net of tax
Beginning balance	(11,816)	(12,072)	(19,850)	(20,244)	(12,072)	(20,244)
Other comprehensive income	256	256	394	394
Ending balance	$ (11,560)	$ (11,816)	$ (19,456)	$ (19,850)	$ (11,560)	$ (19,456)