Note 2 - Investment Securities (Details Textual) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	73
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	$ 37,854		$ 37,087
Debt Securities, Available-for-sale, Realized Gain	69	$ 57
Debt Securities, Available-for-sale, Realized Loss	$ 9	$ 44
US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	19
Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Total	$ 0
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	$ 10,218		9,854
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	29
Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Total	$ 0
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	$ 21,304		23,010
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	2
Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Total	$ 0
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	$ 2,419		1,438
US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	16
Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Total	$ 0
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	$ 3,913		$ 2,785

Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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Amount of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in earnings and other comprehensive loss (OCI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 8A
-URI http://asc.fasb.org/extlink&oid=109979856&loc=SL6284422-111562

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