Note 5 - Financial Instruments Measured at Fair Value - Short-term Investments by Security Type (Details) - USD ($) $ in Thousands		Dec. 25, 2021	Dec. 26, 2020
Amortized cost		$ 89,738	$ 20,668
Gross unrealized gains		2	2
Gross unrealized losses	[1]	36	1
Short-term investments		89,704	20,669
Corporate Debt Securities [Member]
Amortized cost	[2]	84,060	14,943
Gross unrealized gains	[2]	2	2
Gross unrealized losses	[1],[2]	31	1
Short-term investments	[2]	84,031	14,944
US Treasury Securities [Member]
Amortized cost		3,953	2,012
Gross unrealized gains		0	0
Gross unrealized losses	[1]	5	0
Short-term investments		3,948	2,012
Certificates of Deposit [Member]
Amortized cost		800	750
Gross unrealized gains		0	0
Gross unrealized losses	[1]	0	0
Short-term investments		800	750
US Government-sponsored Enterprises Debt Securities [Member]
Amortized cost			1,998
Gross unrealized gains			0
Gross unrealized losses	[1]		0
Short-term investments			1,998
Debt Security, Government, Non-US [Member]
Amortized cost		925	965
Gross unrealized gains		0	0
Gross unrealized losses	[1]	0	0
Short-term investments		$ 925	$ 965

[1] As of December 25, 2021, the cost and fair value of investments with loss positions were approximately $57.0 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 26, 2020, the cost and fair value of investments with loss positions were approximately $8.7 million.

[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.