Note 5 - Stock-based Compensation (Details Textual) - Share-based Payment Arrangement, Nonemployee [Member] - shares shares in Thousands	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period (in shares)	45	13
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period (in shares)	74	79

Number of shares issued under share-based payment arrangement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration