Note 10 - Income Taxes (Details) - Income Tax Reconciliation	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Note 10 - Income Taxes (Details) - Income Tax Reconciliation [Line Items]
Federal statutory rate	35.00%	35.00%	35.00%
Changes from statutory rates resulting from:
Tax credits	0.00%	0.00%	(1.80%)
Company-owned life insurance	(1.90%)	(1.80%)	(3.50%)
Uncertain tax position	(0.30%)	(0.50%)	(0.90%)
Other, net	0.40%	(0.60%)	(0.30%)
Effective tax rate on pretax income	27.00%	24.80%	19.30%
Interest Income [Member]
Changes from statutory rates resulting from:
Tax-exempt interest	(5.20%)	(6.30%)	(7.60%)
Premium income not subject to tax	(5.20%)	(6.30%)	(7.60%)
Interest To Carry Tax Exempt Obligations [Member]
Changes from statutory rates resulting from:
Nondeductible interest to carry tax-exempt obligations	0.20%	0.30%	0.40%
Nondeductible legal expense	0.20%	0.30%	0.40%
Legal Expense [Member]
Changes from statutory rates resulting from:
Nondeductible interest to carry tax-exempt obligations	0.00%	0.00%	0.50%
Nondeductible legal expense	0.00%	0.00%	0.50%
Other Income [Member]
Changes from statutory rates resulting from:
Tax-exempt interest	(1.20%)	(1.30%)	(2.50%)
Premium income not subject to tax	(1.20%)	(1.30%)	(2.50%)