Note 15 - Capital Management and Regulatory Matters - Schedule of the Bank's Actual Capital Amounts and Ratios (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Total risk-based capital to risk weighted assets, actual, amount	$ 126,711		$ 104,186
Total risk-based capital to risk weighted assets, actual, ratio	15.917%		16.449%
Total risk-based capital to risk weighted assets, minimum capital requirement, amount	$ 83,589		$ 66,504
Total risk-based capital to risk weighted assets, minimum capital requirement, ratio	10.50%	8.00%	10.50%
Total risk-based capital to risk weighted assets, minimum to be well capitalized, amount
Total risk-based capital to risk weighted assets, minimum to be well capitalized, ratio
Tier 1 Capital to risk weighted assets, actual amount	$ 108,111		$ 87,586
Tier 1 Capital to risk weighted assets, actual ratio	13.58%		13.829%
Tier 1 Capital to risk weighted assets, minimum capital requirement, amount	$ 67,667		$ 53,836
Tier 1 Capital to risk weighted assets, minimum capital requirement, ratio	8.50%	6.00%	8.50%
Tier 1 Capital to risk weighted assets, minimum to be well capitalized, amount
Tier 1 Capital to risk weighted assets, minimum to be well capitalized , ratio
Common equity tier 1 capital to risk weighted assets, actual, amount	$ 103,111		$ 82,586
Common equity tier 1 capital to risk weighted assets, actual, ratio	12.952%		13.039%
Common equity tier 1 capital to risk weighted assets, minimum capital requirements, amount	$ 55,726		$ 44,336
Common equity tier 1 capital to risk weighted assets, minimum capital requirements, ratio	7.00%	4.50%	7.00%
Common equity tier 1 capital to risk weighted assets, minimum to be well capitalized, amount
Common equity tier 1 capital to risk weighted assets, minimum to be well capitalized, ratio
Tier 1 Capital to adjusted total average assets, actual, amount	$ 108,111		$ 87,586
ier 1 Capital to adjusted total average assets, actual, ratio	10.522%		10.507%
ier 1 Capital to adjusted total average assets, minimum capital requirement, actual	$ 41,099		$ 33,344
Tier 1 Capital to adjusted total average assets, minimum capital requirement, ratio	4.00%		4.00%
Tier 1 Capital to adjusted total average assets, minimum to be well capitalized, actual
Tier 1 Capital to adjusted total average assets, minimum to be well capitalized, ratio
Opportunity Bank of Montana [Member]
Total risk-based capital to risk weighted assets, actual, amount	$ 120,313		$ 100,131
Total risk-based capital to risk weighted assets, actual, ratio	15.231%		16.023%
Total risk-based capital to risk weighted assets, minimum capital requirement, amount	$ 82,944		$ 65,615
Total risk-based capital to risk weighted assets, minimum capital requirement, ratio	10.50%		10.50%
Total risk-based capital to risk weighted assets, minimum to be well capitalized, amount	$ 78,994		$ 62,491
Total risk-based capital to risk weighted assets, minimum to be well capitalized, ratio	10.00%		10.00%
Tier 1 Capital to risk weighted assets, actual amount	$ 111,713		$ 93,531
Tier 1 Capital to risk weighted assets, actual ratio	14.142%		14.967%
Tier 1 Capital to risk weighted assets, minimum capital requirement, amount	$ 67,145		$ 53,117
Tier 1 Capital to risk weighted assets, minimum capital requirement, ratio	8.50%		8.50%
Tier 1 Capital to risk weighted assets, minimum to be well capitalized, amount	$ 63,195		$ 49,993
Tier 1 Capital to risk weighted assets, minimum to be well capitalized , ratio	8.00%		8.00%
Common equity tier 1 capital to risk weighted assets, actual, amount	$ 111,713		$ 93,531
Common equity tier 1 capital to risk weighted assets, actual, ratio	14.142%		14.967%
Common equity tier 1 capital to risk weighted assets, minimum capital requirements, amount	$ 55,296		$ 43,744
Common equity tier 1 capital to risk weighted assets, minimum capital requirements, ratio	7.00%		7.00%
Common equity tier 1 capital to risk weighted assets, minimum to be well capitalized, amount	$ 51,346		$ 40,619
Common equity tier 1 capital to risk weighted assets, minimum to be well capitalized, ratio	6.50%		6.50%
Tier 1 Capital to adjusted total average assets, actual, amount	$ 111,713		$ 93,531
ier 1 Capital to adjusted total average assets, actual, ratio	11.08%		11.222%
ier 1 Capital to adjusted total average assets, minimum capital requirement, actual	$ 40,332		$ 33,338
Tier 1 Capital to adjusted total average assets, minimum capital requirement, ratio	4.00%		4.00%
Tier 1 Capital to adjusted total average assets, minimum to be well capitalized, actual	$ 50,414		$ 41,673
Tier 1 Capital to adjusted total average assets, minimum to be well capitalized, ratio	5.00%		5.00%