Note 2 - Securities - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
US Government-sponsored Enterprises Debt Securities [Member]
Amortized cost	$ 316,763	$ 251,190
Unrealized Gains	4,080	1,468
Unrealized Losses	114	765
Fair value	320,729	251,893
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Amortized cost	158,478	170,139
Unrealized Gains	2,767	1,143
Unrealized Losses	168	1,654
Fair value	161,077	169,628
US States and Political Subdivisions Debt Securities [Member]
Amortized cost	57,979	62,410
Unrealized Gains	1,229	1,342
Unrealized Losses	41	50
Fair value	59,167	63,702
Common Stock [Member]
Amortized cost	653	653
Unrealized Gains	55
Unrealized Losses
Fair value	708	653
US Treasury Securities [Member]
Amortized cost		79,999
Unrealized Gains		1
Unrealized Losses
Fair value		80,000
Amortized cost	533,873	564,391
Unrealized Gains	8,131	3,954
Unrealized Losses	323	2,469
Fair value	$ 541,681	$ 565,876

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
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