GOODWILL AND OTHER INTANGIBLE ASSETS - Changes in carrying amount of goodwill (Details) $ in Thousands	6 Months Ended
	Mar. 31, 2022 USD ($)
Changes in goodwill
Balance as of September 30, 2021	$ 504,853
Acquisition activity and adjustments	6,000
Foreign currency translation	(2,500)
Balance as of March 31, 2022	508,406
USG
Changes in goodwill
Balance as of September 30, 2021	366,500
Acquisition activity and adjustments	300
Foreign currency translation	(2,500)
Balance as of March 31, 2022	364,300
Test
Changes in goodwill
Balance as of September 30, 2021	34,100
Balance as of March 31, 2022	34,100
A&D
Changes in goodwill
Balance as of September 30, 2021	104,300
Acquisition activity and adjustments	5,700
Balance as of March 31, 2022	$ 110,000