GOODWILL AND OTHER INTANGIBLE ASSETS - Changes in carrying amount of goodwill (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2021 USD ($)	Mar. 31, 2021 USD ($)
Changes in goodwill
Goodwill, Beginning Balance		$ 408,063
Acquisition activity		2,500
Foreign currency translation		1,100
Goodwill, Ending Balance	$ 411,661	411,661
Impairment	0	$ 0
Fair value exceeded carrying value percentage		10.00%
Goodwill, Gross	30,000	$ 30,000
USG
Changes in goodwill
Goodwill, Beginning Balance		271,900
Foreign currency translation		1,100
Goodwill, Ending Balance	273,000	273,000
Test
Changes in goodwill
Goodwill, Beginning Balance		34,100
Goodwill, Ending Balance	34,100	34,100
Aerospace & Defense
Changes in goodwill
Goodwill, Beginning Balance		102,100
Acquisition activity		2,500
Goodwill, Ending Balance	$ 104,600	$ 104,600