Note 10 - Federal Income Taxes (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	21.00%	21.00%
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ (100,000)
Deferred Tax Assets, Capital Loss Carryforwards	0	$ 94,000
Unrecognized Tax Benefits, Ending Balance	0	0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	0	0
Firstbank Corporation [Member]
Deferred Tax Assets, Capital Loss Carryforwards	$ 0	$ 100,000