INCOME TAXES - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Deferred tax assets:
Pension and postretirement benefits	$ 11,832	$ 39,705
Accruals and reserves not currently deductible	8,753	12,258
Income tax credit carryforward	5,206	5,308
Operating and capital loss carryforwards	51,438	34,146
Stock options	4,944	4,062
Other	1,320	8,376
Total deferred tax assets	83,493	103,855
Valuation allowances	(28,619)	(22,527)
Net deferred tax assets	54,874	81,328
Deferred tax liabilities:
Depreciation	(23,224)	(27,671)
Unrealized gains and losses	(886)	389
Goodwill and intangible assets	(113,476)	(123,259)
Other	(11,215)	(5,941)
Total deferred tax liabilities	(148,801)	(156,482)
Net deferred tax liability	$ (93,927)	$ (75,154)