Industry Segments - Schedule of Customer Concentration to Consolidated Net Sales (Detail)	3 Months Ended	9 Months Ended
Sep. 27, 2014 Customer	Sep. 28, 2013 Customer	Sep. 27, 2014 Customer	Sep. 28, 2013 Customer
Segment Reporting [Abstract]
Customers individually accounting for more than 10% of consolidated net sales	2	2	2	1
Percentage of consolidated net sales	25.00%	28.00%	26.00%	19.00%

Percentage of consolidated net sales attributable to significant customer.

No definition available.

Name:	cohu_PercentageOfConsolidatedNetSalesAttributableToSignificantCustomer
Namespace Prefix:	cohu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration