Note 6 - Mortgage Loan Servicing - Mortgage Loans Serviced for Others (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Mortgage loans serviced for others	$ 613,631,000	$ 607,890,000
Federal Home Loan Mortgage Corporation [Member]
Mortgage loans serviced for others	600,495,000	597,389,000
Federa lHome Loan Bank [Member]
Mortgage loans serviced for others	$ 13,136,000	$ 10,501,000

Principal amount of transferred financial assets in which the transferor has continuing involvement with the assets underlying the transaction. Continuing involvement includes, but is not limited to, servicing, recourse, and restrictions on transferor's interests in transferred financial assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=d3e107314-111719

Name:	us-gaap_ContinuingInvolvementWithTransferredFinancialAssetsPrincipalAmountOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant