Note 8 - Benefit Plans - Actual and Target Pension Plan Asset Allocation (Details)	Dec. 31, 2019	Dec. 31, 2018
Percentage of plan assets	100.00%	100.00%
Target allocation	100.00%
Equity Securities [Member]
Percentage of plan assets	68.00%	59.00%
Target allocation	60.00%
Fixed Income Investments [Member]
Percentage of plan assets	31.00%	40.00%
Target allocation	40.00%
Other than Securities Investment [Member]
Percentage of plan assets	1.00%	1.00%
Target allocation

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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