Note 1 - Summary of Significant Accounting Policies - Customer Concentration (Details) - Revenue Benchmark [Member] - Customer Concentration Risk [Member]		3 Months Ended
		Mar. 30, 2019		Mar. 31, 2018
Semiconductor Test and Inspection [Member]
Customers individually accounting for more than 10% of net sales	[1]	1		1
Semiconductor Test and Inspection [Member] | One Customer [Member]
Percentage of net sales	[1]	11.00%		12.00%
PCB Test [Member]
Customers individually accounting for more than 10% of net sales	[1]		[2]
Percentage of net sales	[1]		[2]

[1] After the acquisition of Xcerra on October 1, 2018 we report in two segments, Semiconductor Test & Inspection and PCB Test. Cohu's historical reported net sales would have been reported in our Semiconductor Test & Inspection segment and have been presented accordingly.

[2] No single customer represented more than 10% of consolidated net sales.