Note 2 - Accumulated Other Comprehensive Income - Amounts Reclassified Out of Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unrealized gains on available for sale investment securities							$ 3,800
Income tax expense	$ (7,567)	[1]	$ (2,076)	$ (1,722)	$ (1,276)	$ (931)	(1,560)	$ (1,235)	$ (2,715)	$ (12,641)	$ (6,441)	$ (5,293)
Net income	$ (1,435)		$ 5,312	$ 4,482	$ 3,329	$ 2,545	$ 4,324	$ 3,556	$ 6,180	11,688	16,605	14,992
Salaries and employee benefits										(30,296)	(32,296)	(32,008)
Total before tax										24,329	23,046	20,285
Reclassification out of Accumulated Other Comprehensive Income [Member]
Net income										(39)	2,563	51
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Unrealized gains on available for sale investment securities										20	3,998	171
Income tax expense										(7)	(1,399)	(60)
Net income										13	2,599	111
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member]
Salaries and employee benefits										(75)	(50)	(51)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]
Salaries and employee benefits										(5)	(5)	(42)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Income tax expense										28	19	33
Net income										(52)	(36)	(60)
Total before tax										$ (80)	$ (55)	$ (93)

[1] Income tax expense includes $5.9 million related to the remeasurement of the Company's net deferred tax assets due to the change in Federal tax rates.