Note 12 - Other Comprehensive Income (Loss) - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other													$ 4,394	$ 3,001	$ 4,660
Income tax expense	$ 5,542	$ 4,096	$ 4,359	$ 3,142	$ 4,009	$ 3,883	$ 3,676	$ 3,676	$ 4,177	$ 4,352	$ 4,151	$ 4,253	17,139	$ 15,244	16,933
Reclassifications, net of income taxes	$ 4,946	$ 11,704	$ 10,602	$ 10,791	$ 10,616	$ 10,467	$ 10,109	$ 9,835	$ 9,646	$ 9,284	$ 9,002	$ 9,255
Reclassification out of Accumulated Other Comprehensive Income [Member]
Income tax expense													81		36
Reclassifications, net of income taxes													(151)		(67)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Realized loss on sale of available-for-sale securities													(232)
Other															$ (103)