Note 4 - Investment Securities Available-for-Sale (Details) - Securities Available-for-sale by Contractual Maturity (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
U. S. Government agency securities maturing:
Residential mortgage backed securities, amortized cost	$ 377,933	$ 383,665
Residential mortgage backed securities, estimated fair value	382,343	378,133
US Government Agencies Debt Securities [Member]
U. S. Government agency securities maturing:
One year or less, amortized cost	2,998	19,025
One year or less, estimated fair value	3,051	19,133
After one year through five years, amortized cost	19,947	27,615
After one year through five years, estimated fair value	20,276	28,202
Five years through ten years, amortized cost	6,489
Five years through ten years, estimated fair value	6,567
US States and Political Subdivisions Debt Securities [Member]
U. S. Government agency securities maturing:
One year or less, amortized cost	2,410
One year or less, estimated fair value	2,438
After one year through five years, amortized cost	47,038	25,718
After one year through five years, estimated fair value	49,607	26,008
Five years through ten years, amortized cost	54,983	76,705
Five years through ten years, estimated fair value	56,927	75,732
After ten years	2,552
After ten years	2,740
Equity Investment Other [Member]
U. S. Government agency securities maturing:
Residential mortgage backed securities, amortized cost	396	396
Residential mortgage backed securities, estimated fair value	417	384
Residential Mortgage Backed Securities [Member]
U. S. Government agency securities maturing:
Residential mortgage backed securities, amortized cost	241,120	234,206
Residential mortgage backed securities, estimated fair value	$ 240,320	$ 228,674

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing after the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing after the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the next fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of available-for-sale debt securities at fair value that do not have a single maturity date and which the entity has decided to disclose separately rather than allocating the fair value over several maturity groupings.

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