Note 7 - Financial Instruments Measured at Fair Value - Effective Maturities of Short-term Investments (Details) $ in Thousands	Dec. 28, 2019 USD ($)
Due after one year through three years, amortized cost	$ 904
Due after one year through three years, fair value	$ 904

Amount after adjustments of available-for-sale debt securities at cost, maturing in the second fiscal year through the third fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

No definition available.

Name:	cohu_AvailableforsaleSecuritiesDebtMaturitiesYearTwoThroughThreeAmortizedCostBasis
Namespace Prefix:	cohu_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant