Note 4 - Debt and Equity Securities - Securities Available-for-sale and Held-to-maturity by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Securities held-to-maturity, amortized cost, due in one year or less	$ 14,540
Securities held-to-maturity, fair value, due in one year or less	14,540
Securities held-to-maturity, amortized cost, due after ten years	21,866
Securities held-to-maturity, fair value, due after ten years	19,612
Securities held-to-maturity, amortized cost	36,406	$ 37,735
Securities held-to-maturity, fair value	34,152	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	1,766
Securities available for sale, fair value, due after one year through five years	1,774
Securities available for sale, amortized cost, due after five years through ten years	121,217
Securities available for sale, fair value, due after five years through ten years	119,423
Securities available for sale, amortized cost, due after ten years	204,179
Securities available for sale, fair value, due after ten years	203,610
Securities available for sale, amortized cost, total other securities	327,162
Securities available for sale, fair value, total other securities	324,807
Securities available for sale, amortized cost	888,812	868,009
Securities available for sale, fair value	884,143	861,381
Mutual Fund Debt Securities [Member]
Securities available for sale, amortized cost	21,431	21,366
Securities available for sale, fair value	21,431	$ 21,366
Commercial Mortgage Backed Securities [Member]
Securities available for sale, amortized cost	540,219
Securities available for sale, fair value	$ 537,905