Note 16 - Accumulated Other Comprehensive Income - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net (loss) gain on sale of securities		$ (618)			$ (4)		$ (657)		$ (618)	$ (661)	$ 335
Net impairment losses recognized in earnings											4,646
Income before income taxes	11,902	10,218	11,566	11,436	11,933	11,546	9,377	9,257	45,122	42,113	37,945
Income tax expense	2,596	1,118	2,500	2,568	10,720	3,894	2,959	3,055	8,782	20,628	12,819
Net income	$ 9,306	$ 9,100	$ 9,066	$ 8,868	$ 1,213	$ 7,652	$ 6,418	$ 6,202	36,340	21,485	25,126
Net income									713	575	2,865
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member]
Income before income taxes									228	228	226
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]
Income before income taxes									57	31	47
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Income before income taxes									285	259	273
Income tax expense									(60)	(97)	(102)
Net income									225	162	171
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Net (loss) gain on sale of securities									618	661	(335)
Net impairment losses recognized in earnings											4,646
Income before income taxes									618	661	4,311
Income tax expense									(130)	(248)	(1,617)
Net income									$ 488	$ 413	$ 2,694