Note 7 - Shareholders' Equity - Summary of Certain Additional Information about Stock Options (Details) - Share-based Payment Arrangement, Option [Member] - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Weighted average grant-date fair value of options granted during the period (in dollars per share)	$ 1.66	$ 1.35	$ 1.02	$ 1.88
Options in-the-money (in shares) (in shares)	25,344		25,344
Aggregate intrinsic value of options exercised during the period

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration