Note 8 - Subsequent Event (Details Textual) - Xcerra [Member] - USD ($) $ / shares in Units, $ in Millions	Nov. 07, 2018	May 08, 2018
Scenario, Forecast [Member]
Business Combination, Termination Fee by Acquiree	$ 22.8
Scenario, Forecast [Member] | Termination Fee If Cohu Fails to Consummate the Merger [Member]
Business Combination, Termination Fee by Acquiree	$ 45.0
Subsequent Event [Member]
Business Acquisition, Share Price		$ 9
Business Combination, Right to Receive, Per Share, Common Stock		0.2109