Note 4 - Fair Values of Financial Instruments (Details Textual)	9 Months Ended
Sep. 30, 2017 USD ($)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 15,453

Amount of unrealized loss on investments in held-to-maturity securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

Name:	us-gaap_HeldtomaturitySecuritiesContinuousUnrealizedLossPositionAggregateLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration