Note 6 - Debt and Equity Securities - Securities Available-for-sale and Held-to-maturity by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Securities held-to-maturity, amortized cost, due in one year or less	$ 15,870
Securities held-to-maturity, fair value, due in one year or less	15,870
Securities held-to-maturity, amortized cost, due after ten years	21,865
Securities held-to-maturity, fair value, due after ten years	19,538
Securities held-to-maturity, amortized cost	37,735	$ 6,180
Securities held-to-maturity, fair value	35,408	6,180
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	1,781
Securities available for sale, fair value, due after one year through five years	1,784
Securities available for sale, amortized cost, due after five years through ten years	111,348
Securities available for sale, fair value, due after five years through ten years	108,604
Securities available for sale, amortized cost, due after ten years	214,688
Securities available for sale, fair value, due after ten years	213,151
Securities available for sale, amortized cost, total other securities	327,817
Securities available for sale, fair value, total other securities	323,539
Securities available for sale, amortized cost	868,009	994,311
Securities available for sale, fair value	861,381	993,397
Mutual Fund Debt Securities [Member]
Securities available for sale, amortized cost	21,366	21,290
Securities available for sale, fair value	21,366	$ 21,290
Commercial Mortgage Backed Securities [Member]
Securities available for sale, amortized cost	518,826
Securities available for sale, fair value	$ 516,476