EMPLOYEE BENEFIT PLANS - SUMMARY OF CHANGE IN FUNDED STATUS AND LIABILITIES (Details) - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2016
Postemployment employee (liability)
Noncurrent		$ (137,007)		$ (128,888)
Pension
Change in Benefit Obligation
Benefit obligation at beginning of year	[1]	297,835		293,654
Service cost		8,139	[1]	8,347	[1]	$ 7,591
Interest cost		10,493	[1]	9,771	[1]	11,342
Plan participants’ contributions	[1],[2]	45		45
Special termination benefit		3,730	[1],[3]	0	[1],[3]	0
Actuarial (gain) loss	[1]	(12,846)		(5,995)
Benefits paid, net of retiree subsidies received	[1]	(8,821)		(7,987)
Benefit obligation at end of year	[1]	298,575		297,835		293,654
Change in plan assets
Fair value of plan assets at beginning of year	[1]	271,743		249,875
Actual return on plan assets	[1]	16,306		29,736
Employer contributions	[1]	137		74
Benefits paid, net of plan participants’ contributions	[1],[2]	(8,776)		(7,942)
Fair value of plan assets at end of year	[1]	279,410		271,743		249,875
Funded status	[1]	(19,165)		(26,092)
Postemployment employee (liability)
Current	[1]	(294)		(158)
Noncurrent	[1]	(18,871)		(25,934)
Total	[1]	(19,165)		(26,092)
OPEB
Change in Benefit Obligation
Benefit obligation at beginning of year		175,090		160,393
Service cost		4,607		4,380		4,521
Interest cost		6,365		5,545		6,256
Plan participants’ contributions	[2]	161		120
Special termination benefit		490	[3]	0	[3]	0
Actuarial (gain) loss		15,145		8,985
Benefits paid, net of retiree subsidies received		(5,073)		(4,333)
Benefit obligation at end of year		196,785		175,090		160,393
Change in plan assets
Fair value of plan assets at beginning of year		71,534		62,035
Actual return on plan assets		5,284		7,953
Employer contributions		6,222		6,049		3,200
Benefits paid, net of plan participants’ contributions	[2]	(5,060)		(4,503)
Fair value of plan assets at end of year		77,980		71,534		$ 62,035
Funded status		(118,805)		(103,556)
Postemployment employee (liability)
Current		(669)		(602)
Noncurrent		(118,136)		(102,954)
Total		$ (118,805)		$ (103,556)

[1] Includes the Company’s PEP.

[2] Prior to July 1, 1998, employees were eligible to elect an additional participant contribution to enhance their benefits and contributions made during the periods were insignificant.

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