EMPLOYEE BENEFIT PLANS, FAIR VALUE (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Pension
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	[1]	$ 249,875	$ 199,123	$ 211,653
OPEB
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		62,035	57,269	$ 56,909
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		249,875	199,123
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension | Large Cap Index
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		78,306	63,285
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension | Extended Market Index
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		16,250	11,827
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension | International Stock
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		50,702	37,353
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension | Emerging Markets
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		12,906	8,857
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension | Core Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension | Opportunistic Income
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension | Ultra Short Duration
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension | High Yield Bond Fund
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		25,976	20,532
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension | Long Duration Fund
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		65,735	57,269
Quoted Prices in Active Markets for Identical Assets (Level 1) | OPEB
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		62,035	57,269
Quoted Prices in Active Markets for Identical Assets (Level 1) | OPEB | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		9	2,237
Quoted Prices in Active Markets for Identical Assets (Level 1) | OPEB | Large Cap Index
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		19,532	17,460
Quoted Prices in Active Markets for Identical Assets (Level 1) | OPEB | Extended Market Index
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		4,114	3,762
Quoted Prices in Active Markets for Identical Assets (Level 1) | OPEB | International Stock
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		12,997	10,261
Quoted Prices in Active Markets for Identical Assets (Level 1) | OPEB | Emerging Markets
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		3,294	2,617
Quoted Prices in Active Markets for Identical Assets (Level 1) | OPEB | Core Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		7,177	7,148
Quoted Prices in Active Markets for Identical Assets (Level 1) | OPEB | Opportunistic Income
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		4,155	4,179
Quoted Prices in Active Markets for Identical Assets (Level 1) | OPEB | Ultra Short Duration
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		4,082	3,960
Quoted Prices in Active Markets for Identical Assets (Level 1) | OPEB | High Yield Bond Fund
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		6,675	5,645
Quoted Prices in Active Markets for Identical Assets (Level 1) | OPEB | Long Duration Fund
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets		$ 0	$ 0

[1] Includes the Company’s PEP.