Note 2 - Securities - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Securities available-for-sale, amortized cost	$ 571,953	$ 571,936
Securities available-for-sale, unrealized gains	2,154	2,264
Securities available-for-sale, unrealized losses	2,585	4,126
Securities available-for-sale, fair value	571,522	570,074
US Government-sponsored Enterprises Debt Securities [Member]
Securities available-for-sale, amortized cost	372,596	268,784
Securities available-for-sale, unrealized gains	846	800
Securities available-for-sale, unrealized losses	778	1,494
Securities available-for-sale, fair value	372,664	268,090
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities available-for-sale, amortized cost	147,604	170,344
Securities available-for-sale, unrealized gains	697	735
Securities available-for-sale, unrealized losses	1,581	2,236
Securities available-for-sale, fair value	146,720	168,843
US States and Political Subdivisions Debt Securities [Member]
Securities available-for-sale, amortized cost	51,100	57,158
Securities available-for-sale, unrealized gains	611	682
Securities available-for-sale, unrealized losses	89	396
Securities available-for-sale, fair value	51,622	57,444
Common Stock [Member]
Securities available-for-sale, amortized cost	653	653
Securities available-for-sale, unrealized gains		46
Securities available-for-sale, unrealized losses	137
Securities available-for-sale, fair value	$ 516	699
US Treasury Securities [Member]
Securities available-for-sale, amortized cost		74,997
Securities available-for-sale, unrealized gains		1
Securities available-for-sale, unrealized losses
Securities available-for-sale, fair value		$ 74,998

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
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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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.

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-Publisher FASB
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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

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-Publisher FASB
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
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