Note 8 - Benefit Plans - Actual and Target Pension Plan Asset Allocation (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Percentage of plan assets	100.00%	100.00%
Target allocation	100.00%
Equity Securities [Member]
Percentage of plan assets	68.00%	64.00%
Target allocation	68.00%
Fixed Income Investments [Member]
Percentage of plan assets	13.00%	15.00%
Target allocation	13.00%
Other than Securities Investment [Member]
Percentage of plan assets	19.00%	21.00%
Target allocation	19.00%