SHAREHOLDERS' EQUITY - Summary of Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Jun. 30, 2023	Jun. 30, 2022
Rollforward of accumulated other comprehensive income (loss), net of tax
Beginning balance	$ 2,755,806	$ 2,745,145	$ 2,765,472	$ 2,734,410	$ 2,776,591	$ 2,912,618	$ 2,765,472	$ 2,912,618
Other comprehensive income	255	256	256	389	394	394	767	1,177
Ending balance	2,708,081	2,755,806	2,745,145	$ 2,732,668	$ 2,734,410	$ 2,776,591	2,708,081	$ 2,732,668
Unrealized actuarial loss
Rollforward of accumulated other comprehensive income (loss), net of tax
Beginning balance	(11,560)		$ (12,072)				(12,072)
Amounts reclassified from accumulated other comprehensive loss	255						767
Other comprehensive income	255						767
Ending balance	$ (11,305)	$ (11,560)					$ (11,305)