Note 4 - Debt and Equity Securities - Securities Available-for-sale and Held-to-maturity by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Securities held-to-maturity, amortized cost, due in one year or less	$ 1,085
Securities held-to-maturity, fair value, due in one year or less	1,085
Securities held-to-maturity, amortized cost, due after ten years	21,867
Securities held-to-maturity, fair value, due after ten years	20,457
Securities held-to-maturity	30,930	$ 37,735
Securities held-to-maturity, fair value	29,381	35,408
Securities available for sale, amortized cost, due in one year or less	0
Securities available for sale, fair value, due in one year or less	0
Securities available for sale, amortized cost, due after one year through five years	4,335
Securities available for sale, fair value, due after one year through five years	4,443
Securities available for sale, amortized cost, due after five years through ten years	159,666
Securities available for sale, fair value, due after five years through ten years	153,369
Securities available for sale, amortized cost, due after ten years	97,706
Securities available for sale, fair value, due after ten years	100,257
Securities available for sale, amortized cost	800,577	868,009
Securities available for sale, fair value	796,559	861,381
Securities available for sale, amortized cost, total other securities	280,336
Securities available for sale, fair value, total other securities	276,698
Other Debt Obligations [Member]
Securities held-to-maturity	22,952	37,735
Securities held-to-maturity, fair value	21,542	35,408
Securities available for sale, fair value	276,698	344,905
Collateralized Mortgage Backed Securities [Member]
Securities held-to-maturity	7,978
Securities held-to-maturity, fair value	7,839
Securities available for sale, amortized cost	520,241	518,826
Securities available for sale, fair value	519,861	516,476
Mutual Fund Debt Securities [Member]
Securities available for sale, amortized cost	18,629	21,366
Securities available for sale, fair value	18,629	$ 21,366
Commercial Mortgage Backed Securities [Member]
Securities available for sale, amortized cost	520,241
Securities available for sale, fair value	$ 519,861