Note 6 - Investment Securities - The Amortized Cost and Estimated Fair Value of the Securities Portfolio by Contractual Maturity (Details) - USD ($)	Jun. 30, 2016	Dec. 31, 2015
Available-for-sale, amortized cost, due in one year or less	$ 9,601,000
Available-for-sale, estimated fair value, due in one year or less	9,638,000
Held-to-maturity, amortized cost, due in one year or less	0
Held-to-maturity, estimated fair value, due in one year or less	0
Available-for-sale, amortized cost, due after one year through five years	164,845,000
Available-for-sale, estimated fair value, due after one year through five years	166,712,000
Held-to-maturity, amortized cost, due after one year through five years	0
Held-to-maturity, estimated fair value, due after one year through five years	0
Available-for-sale, amortized cost, due after five years through ten years	69,820,000
Available-for-sale, estimated fair value, due after five years through ten years	72,025,000
Held-to-maturity, amortized cost, due after five years through ten years	640,000
Held-to-maturity, estimated fair value, due after five years through ten years	743,000
Available-for-sale, amortized cost, due after ten years	19,233,000
Available-for-sale, estimated fair value, due after ten years	18,560,000
Held-to-maturity, amortized cost, due after ten years	2,945,000
Held-to-maturity, estimated fair value, due after ten years	3,088,000
Available-for-sale, amortized cost, mortgage-backed securities	304,581,000
Available-for-sale, estimated fair value, mortgage-backed securities	312,714,000
Held-to-maturity, amortized cost, mortgage-backed securities	0
Held-to-maturity, estimated fair value, mortgage-backed securities	0
Available-for-sale, amortized cost	568,080,000
Available-for-sale, estimated fair value	579,649,000
Held-to-maturity, amortized cost	3,585,000	$ 3,611,000
Held-to-maturity, estimated fair value	$ 3,831,000	$ 3,809,000