Note 1 - Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018
Net sales	[1]	$ 150,011	$ 99,817	$ 297,820	$ 194,967
Semiconductor Test and Inspection [Member]
Net sales		137,578	99,817	274,272	194,967
PCB Test [Member]
Net sales		12,433		23,548
Systems [Member] | Semiconductor Test and Inspection [Member]
Net sales	[1]	76,155	55,663	156,095	110,568
Systems [Member] | PCB Test [Member]
Net sales	[1]	8,407		15,379
Non-systems [Member] | Semiconductor Test and Inspection [Member]
Net sales	[1]	61,424	44,154	118,177	84,399
Non-systems [Member] | PCB Test [Member]
Net sales	[1]	4,025		8,169
CHINA
Net sales		32,738	19,140	56,289	39,383
UNITED STATES
Net sales		19,408	15,662	36,509	30,140
Malaysia [Member]
Net sales		16,993	13,048	34,707	24,857
TAIWAN, PROVINCE OF CHINA
Net sales		17,202	2,905	32,172	5,846
PHILIPPINES
Net sales		11,395	9,916	25,936	20,462
Rest of the World [Member]
Net sales		$ 52,275	$ 39,146	$ 112,207	$ 74,279

[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.