Note 2 - Acquisitions - Components of Fair Value of Acquisitions and Allocation of Purchase Price For Acquisition of Tennibac-Graphion Inc. (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended		12 Months Ended
	Sep. 30, 2018	Aug. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Jun. 30, 2019
Payments to Acquire Businesses, Net of Cash Acquired, Total			$ (0)	$ 96,828
Goodwill, Ending Balance			281,149		$ 281,149	$ 281,503
Tenibac-Graphion, Inc. [Member]
Payments to Acquire Businesses, Gross	$ 57,284				57,284
Less, cash acquired	(558)				(558)
Payments to Acquire Businesses, Net of Cash Acquired, Total	56,726	$ 57,300			56,726
Other acquired assets	5,023		3,770	5,023	3,770
Other acquired assets					(1,253)
Inventories	324		324	324	324
Inventories, Adjustments					0
Customer Backlog	1,000		200	1,000	200
Customer Backlog, Adjustments					(800)
Property, plant, & equipment	2,490		2,471	2,490	2,471
Property, plant, & equipment, Adjustments					(19)
Identifiable intangible assets	15,960		16,860	15,960	16,860
Identifiable intangible assets, Adjustments					900
Goodwill, Ending Balance	32,949		34,360	32,949	34,360
Goodwill, Adjustments					1,411
Liabilities assumed	$ (1,020)		$ (1,259)	$ (1,020)	(1,259)
Liabilities assumed, Adjustments					$ (239)