Note 12 - Accumulated Other Comprehensive Income (Loss) - Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net loss on sale of securities			$ 657		$ 657
Income before income taxes		11,566	9,377	23,002	18,634
Income tax expense		2,500	2,959	5,068	6,014
Net income		9,066	6,418	17,934	12,620
Reclassification out of Accumulated Other Comprehensive Income [Member]
Net income		56	452	112	492
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Net loss on sale of securities			657		657
Income before income taxes			657		657
Income tax expense			246		246
Net income			411		411
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member]
Amortization	[1]	55	57	114	114
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]
Amortization	[1]	16	8	28	15
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Income before income taxes		71	65	142	129
Income tax expense		15	24	30	48
Net income		$ 56	$ 41	$ 112	$ 81

[1] Amortization is included in net periodic pension cost. See Note 10, "Employee Benefit Plans."