SHARE-BASED COMPENSATION PLANS - Share-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation, Allocation and Classification in Financial Statements [Abstract]
Tax benefit	$ (3,162)	$ (3,767)	$ (4,306)
Total share-based compensation expense, net of tax	13,234	14,460	14,212
Cost of sales
Share-based Compensation, Allocation and Classification in Financial Statements [Abstract]
Share-based compensation expense	2,863	2,727	2,450
Research, development and technical
Share-based Compensation, Allocation and Classification in Financial Statements [Abstract]
Share-based compensation expense	2,090	2,150	1,940
Selling, general and administrative
Share-based Compensation, Allocation and Classification in Financial Statements [Abstract]
Share-based compensation expense	$ 11,443	$ 13,350	$ 14,128