Note 3 - Investment Securities Available-for-Sale (Details) - Securities Available-for-sale by Contractual Maturity (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
U. S. Government agency securities maturing:
Residential mortgage backed securities, amortized cost	$ 328,065	$ 377,933
Residential mortgage backed securities, estimated fair value	333,531	382,343
US Government Agencies Debt Securities [Member]
U. S. Government agency securities maturing:
One year or less, amortized cost	2,999	2,998
One year or less, estimated fair value	3,040	3,051
After one year through five years, amortized cost	19,940	19,947
After one year through five years, estimated fair value	20,381	20,276
Five years through ten years, amortized cost	6,494	6,489
Five years through ten years, estimated fair value	6,698	6,567
US States and Political Subdivisions Debt Securities [Member]
U. S. Government agency securities maturing:
One year or less, amortized cost	1,530	2,410
One year or less, estimated fair value	1,535	2,438
After one year through five years, amortized cost	33,513	47,038
After one year through five years, estimated fair value	36,084	49,607
Five years through ten years, amortized cost	27,505	54,983
Five years through ten years, estimated fair value	28,373	56,927
After ten years	2,561	2,552
After ten years	2,805	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	464	417
Residential Mortgage Backed Securities [Member]
U. S. Government agency securities maturing:
Residential mortgage backed securities, amortized cost	233,127	241,120
Residential mortgage backed securities, estimated fair value	$ 234,151	$ 240,320

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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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Fair value of available-for-sale debt securities maturing in the next 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 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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