Note 5 - Fair Values of Financial Instruments (Details Textual) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	1
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 4

Disclosure regarding factors used to determine that the impairment of securities categorized as held-to-maturity where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the held-to-maturity investments determined to be temporarily impaired.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant