Note 3 - Marketable Securities - Summary of Gross Realized Gains and Losses from Sale of Available-for-sale Marketable Securities (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Gross realized gains from sale of available-for-sale marketable securities	$ 14	$ 13	$ 4
Gross realized losses from sale of available-for-sale marketable securities	$ (20)	$ (41)	$ (71)

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

No definition available.

Name:	us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration