Note 2 - Acquisitions (Details Textual) - USD ($) $ in Thousands			1 Months Ended	3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2019	Sep. 30, 2018	Aug. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2019
Goodwill, Ending Balance	$ 281,503			$ 281,149		$ 281,149	$ 281,149
Payments to Acquire Businesses, Net of Cash Acquired, Total				(0)	$ 96,828
GS Engineering [Member]
Payments to Acquire Businesses, Gross	30,502			30,502		30,500
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total	8,910			8,910		8,910	8,910
Goodwill, Ending Balance	17,976			18,123		18,123	18,123
Payments to Acquire Businesses, Net of Cash Acquired, Total	$ 29,880			29,880
GS Engineering [Member] | Developed Technology Rights [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total				5,600		$ 5,600	5,600
Finite-Lived Intangible Asset, Useful Life						15 years
GS Engineering [Member] | Trademarks [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total				900		$ 900	900
GS Engineering [Member] | Customer Relationships [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total				2,400		$ 2,400	2,400
Finite-Lived Intangible Asset, Useful Life						13 years
Agile Magnetics [Member]
Payments to Acquire Businesses, Gross		$ 39,194					39,194
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total		13,718		17,350	13,718	$ 17,350	17,350
Goodwill, Ending Balance		20,142		16,434	20,142	16,434	16,434
Payments to Acquire Businesses, Net of Cash Acquired, Total		39,193			$ 39,200		39,193
Agile Magnetics [Member] | Trademarks [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total				3,800		3,800	3,800
Agile Magnetics [Member] | Customer Relationships [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total				13,500		13,500	13,500
Finite-Lived Intangible Asset, Useful Life					13 years
Agile Magnetics [Member] | Noncompete Agreements [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total				100		100	100
Finite-Lived Intangible Asset, Useful Life					5 years
Tenibac-Graphion, Inc. [Member]
Payments to Acquire Businesses, Gross		57,284					57,284
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total		15,960		16,860	$ 15,960	16,860	16,860
Goodwill, Ending Balance		32,949		34,360	$ 32,949	34,360	34,360
Payments to Acquire Businesses, Net of Cash Acquired, Total		$ 56,726	$ 57,300				56,726
Business Acquisition, Goodwill, Expected Tax Deductible Amount				34,400		34,400	34,400
Tenibac-Graphion, Inc. [Member] | Trademarks [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total				4,200		4,200	4,200
Tenibac-Graphion, Inc. [Member] | Customer Relationships [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total				11,300		11,300	11,300
Finite-Lived Intangible Asset, Useful Life			15 years
Tenibac-Graphion, Inc. [Member] | Other Intangible Assets [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total				1,400		1,400	1,400
Finite-Lived Intangible Asset, Useful Life			5 years
Horizon Scientific Inc. [Member]
Business Combination, Deferred Compensation Due on Second Anniversary				2,800		2,800	2,800
Business Combination, Deferred Compensation Due on Third Anniversary				5,600		$ 5,600	$ 5,600
Business Combination, Deferred Compensation Arrangements				$ 700