EMPLOYEE BENEFIT PLANS, SUMMARY OF CHANGE IN FUNDED STATUS AND LIABILITIES (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Sep. 30, 2014	Sep. 30, 2015		Sep. 30, 2014		Sep. 30, 2013
Change in Benefit Obligation
Special termination benefits		$ 5,000
Amounts recognized on Consolidated Balance Sheets
Postemployment employee benefit (liability), Noncurrent		(86,674)	$ (137,414)		$ (86,674)
Pension [Member]
Change in Benefit Obligation
Benefit obligation at beginning of year	[1]		227,699		198,826
Service cost			7,485	[1]	6,143	[1]	$ 6,871
Interest cost			10,199	[1]	10,066	[1]	8,942
Plan participants' contributions	[1]		47		47
Special termination benefits			0	[1]	2,814	[1]	0
Actuarial loss	[1]		17,418		21,440
Benefits paid, net of retiree subsidies received	[1]		(6,861)		(11,637)
Benefit obligation at end of year	[1]	227,699	255,987		227,699		198,826
Change in plan assets
Fair value of plan assets at beginning of year	[1]		211,653		200,236
Actual return on plan assets	[1]		(5,813)		22,923
Employer contributions	[1]		97		85
Benefits paid, net of plan participants' contributions	[1]		(6,814)		(11,591)
Fair value of plan assets at end of year	[1]	211,653	199,123		211,653		200,236
Funded status	[1]	(16,046)	(56,864)		(16,046)
Amounts recognized on Consolidated Balance Sheets
Postemployment employee benefit (liability), Current	[1]	(100)	(71)		(100)
Postemployment employee benefit (liability), Noncurrent	[1]	(15,946)	(56,793)		(15,946)
Total	[1]	(16,046)	(56,864)		(16,046)
OPEB [Member]
Change in Benefit Obligation
Benefit obligation at beginning of year			127,773		112,771
Service cost			4,253		3,923		4,686
Interest cost			5,739		5,734		5,148
Plan participants' contributions			60		38
Special termination benefits			0		648		0
Actuarial loss			3,891		6,792
Benefits paid, net of retiree subsidies received			(3,349)		(2,133)
Benefit obligation at end of year		127,773	138,367		127,773		112,771
Change in plan assets
Fair value of plan assets at beginning of year			56,909		49,555
Actual return on plan assets			(1,799)		4,590
Employer contributions			5,672		4,970		6,000
Benefits paid, net of plan participants' contributions			(3,513)		(2,206)
Fair value of plan assets at end of year		56,909	57,269		56,909		$ 49,555
Funded status		(70,864)	(81,098)		(70,864)
Amounts recognized on Consolidated Balance Sheets
Postemployment employee benefit (liability), Current		(136)	(477)		(136)
Postemployment employee benefit (liability), Noncurrent		(70,728)	(80,621)		(70,728)
Total		$ (70,864)	$ (81,098)		$ (70,864)

[1] Includes the Company's PEP.