Note 3 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans - Impaired Loans, Average Investment and Interest Income (Details) - USD ($) $ in Thousands		9 Months Ended			12 Months Ended
		Sep. 30, 2018		Sep. 30, 2017	Dec. 31, 2017
Average recorded investment in impaired loans(1)	[1],[2]	$ 12,684		$ 12,541	$ 13,344	[3]
Interest income recognized on impaired loans, after designation as impaired		414		387	528	[3]
Real Estate Construction Portfolio Segment[Member] | Construction, 1-4 Family Residential [Member]
Average recorded investment in impaired loans(1)	[2],[3]	2,697		3,323	3,298
Interest income recognized on impaired loans, after designation as impaired	[3]	108		133	177
Consumer Real Estate Portfolio Segment [Member] | Closed End First Liens [Member]
Average recorded investment in impaired loans(1)	[2],[3]	891		1,107	781
Interest income recognized on impaired loans, after designation as impaired	[3]	40		30	57
Consumer Real Estate Portfolio Segment [Member] | Closed End Junior Liens [Member]
Average recorded investment in impaired loans(1)	[2],[3]	162		188	185
Interest income recognized on impaired loans, after designation as impaired	[3]	7		8	11
Consumer Real Estate Portfolio Segment [Member] | Investor Owned Residential Real Estate [Member]
Average recorded investment in impaired loans(1)	[2],[3]	661		333	329
Interest income recognized on impaired loans, after designation as impaired	[3]	18		12	1
Commercial Real Estate Portfolio Segment [Member] | Multifamily Real Estate [Member]
Average recorded investment in impaired loans(1)	[2],[3]	298		310	748
Interest income recognized on impaired loans, after designation as impaired	[3]	12		12	16
Commercial Real Estate Portfolio Segment [Member] | Commercial Real Estate, Owner Occupied [Member]
Average recorded investment in impaired loans(1)	[2],[3]	3,934		3,420	4,047
Interest income recognized on impaired loans, after designation as impaired	[3]	145		140	200
Commercial Real Estate Portfolio Segment [Member] | Commercial Real Estate Other [Member]
Average recorded investment in impaired loans(1)	[2],[3]	2,829		2,658	2,638
Interest income recognized on impaired loans, after designation as impaired	[3]	55		45
Commercial Non Real Estate Segment [Member] | Commercial and Industrial [Member]
Average recorded investment in impaired loans(1)	[2],[3]	1,188		1,187	1,282
Interest income recognized on impaired loans, after designation as impaired	[3]	28		6	64
Consumer Non Real Estate Portfolio Segment [Member] | Automobile Loan [Member]
Average recorded investment in impaired loans(1)	[2]	24	[3]	15	36
Interest income recognized on impaired loans, after designation as impaired		$ 1	[3]	$ 1	$ 2	[3]

[1] Recorded investment is net of charge-offs and interest paid while a loan is in nonaccrual status.

[2] Recorded investment is net of charge-offs and interest paid while a loan is in nonaccrual status.

[3] Only classes with impaired loans are shown.