Note 5 - Financial Instruments Measured at Fair Value - Short-term Investments by Security Type (Details) - USD ($) $ in Thousands		Sep. 25, 2021	Dec. 26, 2020
Amortized cost		$ 76,012	$ 20,668
Gross unrealized gains		11	2
Gross unrealized losses	[1]	3	1
Short-term investments		76,020	20,669
Corporate Debt Securities [Member]
Amortized cost	[2]	68,333	14,943
Gross unrealized gains	[2]	10	2
Gross unrealized losses	[1],[2]	3	1
Short-term investments	[2]	68,340	14,944
US Treasury Securities [Member]
Amortized cost		3,216	2,012
Gross unrealized gains		0	0
Gross unrealized losses	[1]	0	0
Short-term investments		3,216	2,012
US Government-sponsored Enterprises Debt Securities [Member]
Amortized cost		2,000	1,998
Gross unrealized gains		0	0
Gross unrealized losses	[1]	0	0
Short-term investments		2,000	1,998
Certificates of Deposit [Member]
Amortized cost		1,550	750
Gross unrealized gains		1	0
Gross unrealized losses	[1]	0	0
Short-term investments		1,551	750
Debt Security, Government, Non-US [Member]
Amortized cost		913	965
Gross unrealized gains		0	0
Gross unrealized losses	[1]	0	0
Short-term investments		$ 913	$ 965

[1] As of September 25, 2021 and December 26, 2020, the cost and fair value of investments with loss positions were approximately $21.3 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] 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.