Note 6 - Marketable Securities - Summary of Gross Unrealized Losses and Fair Values on Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Less than 12 months, Fair value	$ 26,707	$ 31,393
Less than 12 months, Gross unrealized loss	(250)	(91)
12 months or greater, Fair value	991	7,381
12 months or greater, Gross unrealized loss	$ (10)	$ (21)

This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

No definition available.

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