Note 11 - Federal Income Taxes (Details Textual) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	35.00%	35.00%
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability	$ 1,300,000	$ 0	$ 1,336,000	$ 0
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount		(100,000)	(100,000)
Deferred Tax Assets, Capital Loss Carryforwards	94,000	94,000	94,000
Unrecognized Tax Benefits, Ending Balance	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	0	0	0
Firstbank Corporation [Member]
Deferred Tax Assets, Capital Loss Carryforwards	$ 100,000	$ 100,000	$ 100,000