Note 14 - Employee Benefits - Stock Option Activity (Details) - $ / shares	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Outstanding, January 1 (in shares)	29,324	31,949
Outstanding, January 1 (in dollars per share)	$ 23.67
Expired (in shares)	(1,337)
Expired (in dollars per share)	$ 37.48
Exercised (in shares)	(8,237)	(500)
Exercised (in dollars per share)	$ 27.97
Outstanding, December 31 (in shares)	19,750	29,324
Outstanding, December 31 (in dollars per share)	$ 20.94	$ 23.67
Exercisable, December 31 (in shares)	19,750
Exercisable, December 31 (in dollars per share)	$ 20.94

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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-Name Accounting Standards Codification
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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Number of share options (or share units) exercised during the current period.

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