Note 11 - Federal Income Taxes - Consolidated Income Tax Expense (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current expense		$ 10,170,000	$ 13,978,000	$ 15,786,000
Deferred expense		(372,000)	(505,000)	(699,000)
Effect of federal tax law change	$ 1,300,000	0	1,336,000	0
Change in valuation allowance		0	0	(113,000)
Federal income tax benefit		$ 9,798,000	$ 14,809,000	$ 14,974,000