Note 10 - Retirement Plans (Details Textual)	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	7.50%	7.50%
Company Matching Percentage on First Six Percent of Employee Contributions	50.00%
Employee Contribution Percentage for Which Company Will Match at Fifty Percent	6.00%
Defined Contribution Plan Number of Investment Options	15
Number of Non-contributory Defined Benefit Plans	2
Pension and Other Postretirement Defined Benefit Plans, Liabilities	$ 1,900,000	$ 2,100,000
Accumulated Other Comprehensive Income Loss Unrecognized Net Actuarial Losses Net of Tax	1,600,000	1,900,000
Defined Benefit Plan, Accumulated Benefit Obligation	6,400,000	6,900,000
Defined Benefit Plan, Fair Value of Plan Assets	4,500,000	4,800,000
Defined Benefit Plan, Net Periodic Benefit Cost	$ 400,000	$ 200,000	$ 400,000
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.91%	3.54%
Company Matching Percentage on First Ten Thousand Dollar Employee Contributions	50.00%
Officer Contribution for Which Company Will Match at Fifty Percent	$ 10,000
Select Employee Contribution for Which Company Will Match at Fifty Percent	$ 5,000
Retirement Target Benefit Plan, Percentage of Final Base Pay after 35-year Career	35.00%
Retirement Target Benefit Plan, Percentage of Final Base Pay per Year of Service	1.00%
Non-qualified Retirement Savings Plan Actuarial Yearly Asset Growth Percentage Assumption	8.00%
Deferred Compensation Liability, Current and Noncurrent	$ 6,400,000	$ 6,600,000
Retirement Plan Expense	$ 1,500,000	$ 1,800,000	$ 1,800,000