Note 15 - Regulatory Capital Requirements - Capital and Capital Ratio Information (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Jun. 30, 2016
California First National Bancorp [Member]
Total risk-based capital, ratio	34.30%	26.04%
Tier 1 leverage capital	$ 196,140	$ 189,677
Tier 1 leverage capital, ratio	26.01%	21.67%
Common equity Tier 1 capital	$ 196,140	$ 189,677
Common equity Tier 1 capital, ratio	33.09%	25.12%
Tier 1 risk-based capital	$ 196,140	$ 189,677
Tier 1 risk-based capital, ratio	33.09%	25.12%
Total risk-based capital	$ 203,338	$ 196,589
California First National Bank [Member]
Total risk-based capital, ratio	23.45%	16.79%
Tier 1 leverage capital	$ 126,424	$ 116,379
Tier 1 leverage capital, ratio	17.23%	13.94%
Common equity Tier 1 capital	$ 126,424	$ 116,379
Common equity Tier 1 capital, ratio	22.22%	15.88%
Tier 1 risk-based capital	$ 126,424	$ 116,379
Tier 1 risk-based capital, ratio	22.22%	15.88%
Total risk-based capital	$ 133,419	$ 123,091