Note 3 - Investment Securities - Amortized Costs and Estimated Fair Value of the Securities Portfolio (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Available for Sale Securities - Amortized Cost	$ 428,695	$ 486,038
Available for Sale Securities - Gross Unrealized Gains	1,252	2,518
Available for Sale Securities - Gross Unrealized Losses	5,694	7,692
Available for Sale Securities - Estimated Fair Value	424,253	480,864
Held to Maturity Securities - Amortized Cost	3,364	3,488
Held to Maturity Securities - Estimated Fair Value	3,478	3,597
US Government-sponsored Enterprises Debt Securities [Member]
Available for Sale Securities - Amortized Cost	43,601	71,941
Available for Sale Securities - Gross Unrealized Gains	44	213
Available for Sale Securities - Gross Unrealized Losses	437	460
Available for Sale Securities - Estimated Fair Value	43,208	71,694
US States and Political Subdivisions Debt Securities [Member]
Available for Sale Securities - Amortized Cost	114,960	134,055
Available for Sale Securities - Gross Unrealized Gains	562	773
Available for Sale Securities - Gross Unrealized Losses	1,273	2,536
Available for Sale Securities - Estimated Fair Value	114,249	132,292
Held to Maturity Securities - Amortized Cost	3,364	3,488
Held to Maturity Securities - Gross Unrealized Gains	114	109
Held to Maturity Securities - Gross Unrealized Losses	0	0
Held to Maturity Securities - Estimated Fair Value	3,478	3,597
Residential Mortgage Backed Securities [Member]
Available for Sale Securities - Amortized Cost	195,605	225,489
Available for Sale Securities - Gross Unrealized Gains	523	1,505
Available for Sale Securities - Gross Unrealized Losses	2,735	2,687
Available for Sale Securities - Estimated Fair Value	193,393	224,307
Commercial Mortgage Backed Securities [Member]
Available for Sale Securities - Amortized Cost	50,518	47,164
Available for Sale Securities - Gross Unrealized Gains	42	6
Available for Sale Securities - Gross Unrealized Losses	1,208	1,557
Available for Sale Securities - Estimated Fair Value	49,352	45,613
Asset-backed Securities [Member]
Available for Sale Securities - Amortized Cost	15,569
Available for Sale Securities - Gross Unrealized Gains	9
Available for Sale Securities - Gross Unrealized Losses	4
Available for Sale Securities - Estimated Fair Value	15,574
Corporate Debt Securities [Member]
Available for Sale Securities - Amortized Cost	7,578	6,565
Available for Sale Securities - Gross Unrealized Gains	1	1
Available for Sale Securities - Gross Unrealized Losses	37	441
Available for Sale Securities - Estimated Fair Value	7,542	6,125
Mutual Funds and Equity Securities [Member]
Available for Sale Securities - Amortized Cost	864	824
Available for Sale Securities - Gross Unrealized Gains	71	20
Available for Sale Securities - Gross Unrealized Losses	0	11
Available for Sale Securities - Estimated Fair Value	$ 935	$ 833

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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