Note 6 - Marketable Securities - Summary of Gross Realized Gains and Losses from Sale of Available-for-sale Marketable Securities (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Gross realized gains from sale of available-for-sale marketable securities	$ 43	$ 0	$ 43	$ 4
Gross realized losses from sale of available-for-sale marketable securities	$ (28)	$ (13)	$ (28)	$ (19)

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