EMPLOYEE BENEFIT PLANS - Plan assets and benefit obligation of the defined benefit plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Change in plan assets:
Fair value of plan assets at beginning of fiscal year	$ 147,145
Fair value of plan assets at end of fiscal year	160,523	$ 147,145
Pension Plan
Change in benefit obligation:
Benefit obligation at beginning of fiscal year	183,003	177,797
Interest cost	2,816	4,267	$ 5,778
Benefits paid	(10,743)	(10,747)
Actuarial (gain) loss	(4,571)	11,686
Benefit obligation at end of fiscal year	170,505	183,003	177,797
Change in plan assets:
Fair value of plan assets at beginning of fiscal year	147,145	145,610
Actual return on plan assets	23,199	4,261
Company contributions	922	8,021
Benefits paid	(10,743)	(10,747)
Fair value of plan assets at end of fiscal year	160,523	147,145	145,610
Projected benefit obligation in excess of plan assets	(9,982)	(35,858)
Amounts recognized in the statement of financial position consist of:
Accrued liabilities	0	0
Other liabilities (long-term)	(9,982)	(35,858)
Total Liabilities	(9,982)	(35,858)
Net actuarial losses	38,296	61,666
Prior service cost	0	0
Deferred taxes	(8,042)	(12,950)
Total Accumulated other comprehensive loss, net of tax	30,254	48,716
Net amount recognized at September 30,	20,272	12,858
Accumulated benefit obligations	170,505	183,003
Information for plans with accumulated benefit obligations in excess of plan assets:
ABO	170,505	183,003
PBO	170,505	183,003
Fair value of plan assets	160,523	147,145
Supplemental Employee Retirement Plan
Change in benefit obligation:
Benefit obligation at beginning of fiscal year	16,070	16,180
Interest cost	162	335	503
Benefits paid	(1,936)	(1,939)
Actuarial (gain) loss	479	1,494
Benefit obligation at end of fiscal year	14,775	16,070	16,180
Change in plan assets:
Fair value of plan assets at beginning of fiscal year	0	0
Actual return on plan assets	0	0
Company contributions	1,936	1,939
Benefits paid	(1,936)	(1,939)
Fair value of plan assets at end of fiscal year	0	0	$ 0
Projected benefit obligation in excess of plan assets	(14,775)	(16,070)
Amounts recognized in the statement of financial position consist of:
Accrued liabilities	(1,884)	(1,891)
Other liabilities (long-term)	(12,890)	(14,179)
Total Liabilities	(14,774)	(16,070)
Net actuarial losses	7,662	7,700
Prior service cost	0	0
Deferred taxes	(1,609)	(1,617)
Total Accumulated other comprehensive loss, net of tax	6,053	6,083
Net amount recognized at September 30,	(8,721)	(9,987)
Accumulated benefit obligations	14,775	16,070
Information for plans with accumulated benefit obligations in excess of plan assets:
ABO	14,775	16,070
PBO	14,775	16,070
Fair value of plan assets	$ 0	$ 0