EMPLOYEE BENEFIT PLANS - COMPONENTS OF NET PERIODIC COST (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2016
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 8,139	[1]	$ 8,347	[1]	$ 7,591
Interest cost	10,493	[1]	9,771	[1]	11,342
Expected return on plan assets	(19,639)		(19,313)		(20,118)
Recognized actuarial loss	7,537		8,827		7,281
Prior service cost (credit) amortization	106		111		111
Net periodic benefit cost	6,636		7,743		6,207
Special termination benefit	3,730	[1],[2]	0	[1],[2]	0
Net periodic benefit cost recognized as expense	10,366		7,743		6,207
OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	4,607		4,380		4,521
Interest cost	6,365		5,545		6,256
Expected return on plan assets	(5,352)		(4,767)		(4,845)
Recognized actuarial loss	4,660		4,370		3,274
Prior service cost (credit) amortization	(365)		(365)		(365)
Net periodic benefit cost	9,915		9,163		8,841
Special termination benefit	490	[2]	0	[2]	0
Net periodic benefit cost recognized as expense	$ 10,405		$ 9,163		$ 8,841

[1] Includes the Company’s PEP.

[2] Related to the voluntary early retirement program offered during fiscal 2018, as previously discussed.