Note 4 - Securities Available for Sale (Details Textual) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Proceeds from Sale of Available-for-sale Securities	$ 0	$ 20,000	$ 10,951,000
Gain (Loss) on Sale of Securities, Net	0	(10,000)	6,000
Available-for-sale Securities [Member]
Gain (Loss) on Sale of Securities, Net	$ 0	$ (10,000)	$ 6,000

The net gain (loss) realized from the sale, exchange, redemption, or retirement of securities, not separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13(h))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.3)
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration