Note 7 - Financial Instruments Measured at Fair Value - Short-term Investments by Security Type (Details) - USD ($) $ in Thousands		Dec. 26, 2020	Dec. 28, 2019
Amortized Cost		$ 20,668
Gross Unrealized Gains		2
Gross Unrealized Losses	[1]	1
Estimated Fair Value		20,669	$ 904
Corporate Debt Securities [Member]
Amortized Cost	[2]	14,943
Gross Unrealized Gains	[2]	2
Gross Unrealized Losses	[1],[2]	1
Estimated Fair Value	[2]	14,944
Debt Security, Government, Non-US [Member]
Amortized Cost		965	904
Gross Unrealized Gains		0	0
Gross Unrealized Losses	[1]	0	0
Estimated Fair Value		965	$ 904
US Treasury Securities [Member]
Amortized Cost		2,012
Gross Unrealized Gains		0
Gross Unrealized Losses	[1]	0
Estimated Fair Value		2,012
US Government-sponsored Enterprises Debt Securities [Member]
Amortized Cost		1,998
Gross Unrealized Gains		0
Gross Unrealized Losses	[1]	0
Estimated Fair Value		1,998
Certificates of Deposit [Member]
Amortized Cost		750
Gross Unrealized Gains		0
Gross Unrealized Losses	[1]	0
Estimated Fair Value		$ 750

[1] As of December 26, 2020, the cost and fair value of investments with loss positions were approximately $8.7 million. We evaluated the nature of these investments, credit worthiness of the issuer and the duration of these impairments to determine if an other-than-temporary decline in fair value had occurred and concluded that these losses were temporary and we have the ability and intent to hold these investments to maturity. As of December 28, 2019, we had no investments with loss positions.

[2] Corporate debt securities include investments in financial and other corporate institutions. No single issuer represents a significant portion of the total corporate debt securities portfolio.