Note 5 - Financial Instruments Measured at Fair Value - Short-term Investments by Security Type (Details) - USD ($) $ in Thousands		Mar. 27, 2021	Dec. 26, 2020
Amortized Cost		$ 147,920	$ 20,668
Gross Unrealized Gains		17	2
Gross Unrealized Losses	[1]	11	1
Estimated Fair Value		147,926	20,669	[2]
Corporate Debt Securities [Member]
Amortized Cost	[3]	136,400	14,943
Gross Unrealized Gains	[3]	16	2
Gross Unrealized Losses	[1],[3]	11	1
Estimated Fair Value	[3]	136,405	14,944
US Treasury Securities [Member]
Amortized Cost		7,811	2,012
Gross Unrealized Gains		0	0
Gross Unrealized Losses	[1]	0	0
Estimated Fair Value		7,811	2,012
US Government-sponsored Enterprises Debt Securities [Member]
Amortized Cost		1,999	1,998
Gross Unrealized Gains		1	0
Gross Unrealized Losses	[1]	0	0
Estimated Fair Value		2,000	1,998
Certificates of Deposit [Member]
Amortized Cost		750	750
Gross Unrealized Gains		0	0
Gross Unrealized Losses	[1]	0	0
Estimated Fair Value		750	750
Debt Security, Government, Non-US [Member]
Amortized Cost		960	965
Gross Unrealized Gains		0	0
Gross Unrealized Losses	[1]	0	0
Estimated Fair Value		$ 960	$ 965

[1] As of March 27, 2021 and December 26, 2020, the cost and fair value of investments with loss positions were approximately $61.6 million and $8.7 million, respectively. 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.

[2] Derived from December 26, 2020 audited financial statements

[3] 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.