Goodwill and Other Intangible Assets - Changes in carrying amount of goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Changes in goodwill
Goodwill, Beginning Balance	$ 381,652	$ 377,900
Acquisition activity	28,500	3,900
Foreign currency translation	(1,000)	(100)
Goodwill, Ending Balance	409,215	381,652
USG
Changes in goodwill
Goodwill, Beginning Balance	254,100	250,200
Acquisition activity	0	3,900
Foreign currency translation	(100)	0
Goodwill, Ending Balance	254,000	254,100
Test
Changes in goodwill
Goodwill, Beginning Balance	34,100	34,100
Acquisition activity	0	0
Foreign currency translation	0	0
Goodwill, Ending Balance	34,100	34,100
Filtration
Changes in goodwill
Goodwill, Beginning Balance	73,700	73,700
Acquisition activity	28,500	0
Foreign currency translation	0	0
Goodwill, Ending Balance	102,200	73,700
Technical Packaging
Changes in goodwill
Goodwill, Beginning Balance	19,800	19,900
Acquisition activity	0	0
Foreign currency translation	(900)	(100)
Goodwill, Ending Balance	$ 18,900	$ 19,800