Note 6 - Investment Securities - The Amortized Cost and Estimated Fair Value of the Securities Portfolio by Contractual Maturity (Details) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Available-for-sale, amortized cost, due in one year or less	$ 13,318,000
Available-for-sale, estimated fair value, due in one year or less	13,343,000
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	92,602,000
Available-for-sale, estimated fair value, due after one year through five years	93,694,000
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	77,762,000
Available-for-sale, estimated fair value, due after five years through ten years	78,931,000
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	737,000
Available-for-sale, amortized cost, due after ten years	17,636,000
Available-for-sale, estimated fair value, due after ten years	17,174,000
Held-to-maturity, amortized cost, due after ten years	2,932,000
Held-to-maturity, estimated fair value, due after ten years	3,064,000
Available-for-sale, amortized cost, mortgage-backed securities	266,862,000
Available-for-sale, estimated fair value, mortgage-backed securities	270,462,000
Held-to-maturity, amortized cost, mortgage-backed securities	0
Held-to-maturity, estimated fair value, mortgage-backed securities	0
Available-for-sale, amortized cost	468,180,000
Available-for-sale, estimated fair value	473,604,000
Held-to-maturity, amortized cost	3,572,000	$ 3,611,000
Held-to-maturity, estimated fair value	$ 3,801,000	$ 3,809,000