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Note 6 - Share-based Payments - Summary of Stock Performance Awards Granted and Amounts Expensed (Details) - Executive Officer [Member] - Stock Performance Awards [Member] - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Compensation Expense Recognized	$ 3,597,000	$ 2,645,000	$ 2,007,000
Earned Shares (in shares)	297,943
Performance Period 2019 To 2021 [Member]
Maximum Shares Subject to Award (in shares)	83,400
Target Shares (in shares)	55,600
Compensation Expense Recognized	$ 2,168,000
Performance Period 2018 To 2020 [Member]
Maximum Shares Subject to Award (in shares)	81,000
Target Shares (in shares)	54,000
Compensation Expense Recognized	$ 897,000	1,121,000
Performance Period 2017 To 2019 [Member]
Maximum Shares Subject to Award (in shares)	89,250
Target Shares (in shares)	59,500
Compensation Expense Recognized	$ 524,000	729,000	854,000
Earned Shares (in shares)	69,997
Performance Period 2016 To 2018 [Member]
Maximum Shares Subject to Award (in shares)	122,250
Target Shares (in shares)	81,500
Compensation Expense Recognized	$ 8,000	772,000	580,000
Earned Shares (in shares)	113,298
Performance Period 2015 To 2017 [Member]
Maximum Shares Subject to Award (in shares)	126,450
Target Shares (in shares)	84,300
Compensation Expense Recognized	$ 0	$ 23,000	$ 573,000
Earned Shares (in shares)	114,648

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+ References

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+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
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Number of shares authorized for issuance under share-based payment arrangement.

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