INCOME TAXES - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Deferred tax assets:
Pension and postretirement benefits	$ 37,587	$ 24,597
Accruals and reserves not currently deductible	10,400	9,596
Income tax credit carryforward	3,204	3,216
Operating and capital loss carryforwards	21,896	21,858
Stock options	4,778	5,157
Other	5,381	3,963
Total deferred tax assets	83,246	68,387
Valuation allowances	(15,352)	(15,188)
Net deferred tax assets	67,894	53,199
Deferred tax liabilities:
Depreciation	(24,792)	(16,156)
Unrealized gains and losses	(565)	(8,637)
Goodwill and intangible assets	(138,952)	(147,571)
Other	(1,035)	(517)
Deferred tax liabilities	(165,344)	(172,881)
Net deferred tax liability	$ (97,450)	$ (119,682)