Note 11 - Federal Income Taxes - Consolidated Income Tax Expense (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current expense		$ 13,978,000	$ 15,786,000	$ 7,399,000
Deferred expense		(505,000)	(699,000)	4,592,000
Effect of federal tax law change	$ 1,300,000	1,336,000	0	0
Change in valuation allowance		0	(113,000)	(180,000)
Tax expense		$ 14,809,000	$ 14,974,000	$ 11,811,000