Note 12 - Other Comprehensive Income (Loss) - Reclassifications out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($)	3 Months Ended												12 Months Ended
	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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Realized loss on sale of available-for-sale securities														$ 0
Other													$ 12,610,000	13,316,000	$ 13,012,000
Income tax expense	$ 4,009,000	$ 3,883,000	$ 3,676,000	$ 3,676,000	$ 4,177,000	$ 4,352,000	$ 4,151,000	$ 4,253,000	$ 3,307,000	$ 4,715,000	$ 3,627,000	$ 3,632,000	15,244,000	16,933,000	15,281,000
Reclassifications, net of income taxes	$ 10,616,000	$ 10,467,000	$ 10,109,000	$ 9,835,000	$ 9,646,000	$ 9,284,000	$ 9,002,000	$ 9,255,000	$ 8,722,000	$ 9,889,000	$ 8,034,000	$ 8,177,000
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															(9,000)
Other														(103,000)
Income tax expense														36,000	3,000
Reclassifications, net of income taxes														$ (67,000)	$ (6,000)