Note 11 - Fair Value of Financial Instruments and Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis (Details) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Impaired Loans [Member]
Assets, fair value, nonrecurring	$ 6,090,000	$ 6,952,000
Other Real Estate [Member]
Assets, fair value, nonrecurring	1,857,000	2,505,000
Fair Value, Inputs, Level 3 [Member] | Impaired Loans [Member]
Assets, fair value, nonrecurring	6,090,000	6,952,000
Fair Value, Inputs, Level 3 [Member] | Other Real Estate [Member]
Assets, fair value, nonrecurring	1,857,000	2,505,000
Available-for-sale Securities [Member]
Assets, fair value, recurring	337,710,000	323,658,000
Available-for-sale Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets, fair value, recurring	337,134,000	323,082,000
Available-for-sale Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets, fair value, recurring	576,000	576,000
US Government Agencies Debt Securities [Member] | Available-for-sale Securities [Member]
Assets, fair value, recurring	330,742	319,097
US Government Agencies Debt Securities [Member] | Available-for-sale Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets, fair value, recurring
US Government Agencies Debt Securities [Member] | Available-for-sale Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets, fair value, recurring	330,742	319,097
US Government Agencies Debt Securities [Member] | Available-for-sale Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets, fair value, recurring
US States and Political Subdivisions Debt Securities [Member] | Available-for-sale Securities [Member]
Assets, fair value, recurring	4,904,000	4,561,000
US States and Political Subdivisions Debt Securities [Member] | Available-for-sale Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets, fair value, recurring	4,328,000	3,985,000
US States and Political Subdivisions Debt Securities [Member] | Available-for-sale Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets, fair value, recurring	576,000	$ 576,000
Corporate Debt Securities [Member] | Available-for-sale Securities [Member]
Assets, fair value, recurring	2,064,000
Corporate Debt Securities [Member] | Available-for-sale Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets, fair value, recurring	$ 2,064,000