EMPLOYEE BENEFIT PLANS (Details) - USD ($)	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Apr. 30, 2018
Components of net periodic cost
Discretionary contribution			$ 0
Postemployment benefits, expected future benefit payment					$ 6,400,000
Postemployment benefits, period expense			4,600,000
Pension
Components of net periodic cost
Service cost	$ 2,035,000	$ 2,086,000	6,104,000	$ 6,260,000
Interest cost	2,623,000	2,443,000	7,870,000	7,328,000
Expected return on plan assets	(4,910,000)	(4,829,000)	(14,729,000)	(14,485,000)
Recognized actuarial loss	1,884,000	2,207,000	5,653,000	6,620,000
Prior service cost amortization	27,000	28,000	80,000	83,000
Net periodic benefit cost	1,659,000	1,935,000	4,978,000	5,806,000
OPEB
Components of net periodic cost
Service cost	1,152,000	1,095,000	3,455,000	3,285,000
Interest cost	1,591,000	1,386,000	4,773,000	4,159,000
Expected return on plan assets	(1,338,000)	(1,192,000)	(4,014,000)	(3,575,000)
Recognized actuarial loss	1,165,000	1,093,000	3,495,000	3,278,000
Prior service cost amortization	(91,000)	(91,000)	(273,000)	(273,000)
Net periodic benefit cost	$ 2,479,000	$ 2,291,000	$ 7,436,000	$ 6,874,000