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	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			35.00%	35.00%	35.00%
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability	$ 1,300,000		$ 1,336,000	$ 0	$ 0
Deferred Tax Assets, Valuation Allowance	94,000		94,000	157,000
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount			0	(100,000)
Deferred Tax Assets, Capital Loss Carryforwards	94,000		94,000	157,000
Unrecognized Tax Benefits	0		0	0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	0		0	$ 0
Firstbank Corporation [Member]
Deferred Tax Assets, Capital Loss Carryforwards	$ 100,000		$ 100,000
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%