Note 6 - Investments (Details)	Dec. 31, 2015
Investments Schedule [Abstract]
Percentage of Capital Surplus Equal to Federal Reserve Bank Stock, Required to Hold	6.00%

The percentage of capital surplus, which is defined as additional paid-in capital less any gains (losses) on available-for-sale securities as of the current period, equal to Federal Reserve Bank stock that the company is required to hold.

No definition available.

Name:	cfnb_PercentageOfCapitalSurplusEqualToFederalReserveBankStockRequiredToHold
Namespace Prefix:	cfnb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant