Note 8 - Benefit Plans - Actual and Target Pension Plan Asset Allocation (Details)	Dec. 31, 2017	Dec. 31, 2016
Percentage of plan assets	100.00%	100.00%
Target allocation	100.00%
Equity Securities [Member]
Percentage of plan assets	52.00%	68.00%
Target allocation	52.00%
Fixed Income Investments [Member]
Percentage of plan assets	29.00%	13.00%
Target allocation	29.00%
Other than Securities Investment [Member]
Percentage of plan assets	19.00%	19.00%
Target allocation	19.00%

Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2446-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Data Type:	num:percentItemType
Balance Type:	na
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