Note 6 - Accrued Retirement Benefits - Summary of Assumptions Used (Details)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Discount rate		4.28%
Expected long-term return on plan assets	4.75%	5.00%
Minimum [Member]
Discount rate	3.10%
Expected long-term return on plan assets
Maximum [Member]
Discount rate	3.14%
Expected long-term return on plan assets

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2919-114920

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration