Note 5 - Financial Instruments Measured at Fair Value (Details Textual) - USD ($) $ in Millions	Mar. 27, 2021	Dec. 26, 2020
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	$ 61.6	$ 8.7

This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

No definition available.

Name:	us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant