Note 5 - Securities - (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale Securities Pledged as Collateral	$ 103,200,000	$ 86,000,000
Available-for-sale Securities, Gross Realized Gains	31,000	260,000	$ 3,000
Available-for-sale Securities, Gross Realized Losses	0	28,000	$ 18,000
Other Equity Securities, Fair Value Disclosure	8,627,000	6,120,000
The Independent Bankers Bank [Member]
Other Equity Securities, Fair Value Disclosure	100,000	100,000
Mc Larty Capital Partners SBIC L.P [Member]
Other Equity Securities, Fair Value Disclosure	1,800,000	1,600,000
Bluehenge Capital Secured Debt SBIC L.P [Member]
Other Equity Securities, Fair Value Disclosure	654,000	348,000
Bankers Insurance LLC [Member]
Other Equity Securities, Fair Value Disclosure	226,000	234,000
First National Bankers Bank [Member]
Other Equity Securities, Fair Value Disclosure	252,000	252,000
McLarty Capital Partners SBIC II, L.P. [Member]
Other Equity Securities, Fair Value Disclosure	1,600,000
New Louisiana Angel Fund 2, LLC [Member]
Other Equity Securities, Fair Value Disclosure	13,000
Federal Home Loan Bank of Dallas [Member]
Other Equity Securities, Fair Value Disclosure	$ 4,000,000	$ 3,600,000