Note 6 - Loans and the Allowance for Loan Losses - Allowance for Credit Losses and Recorded Investment in Loans Receivable (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended			12 Months Ended
		Sep. 30, 2018		Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017	Dec. 31, 2017		Dec. 31, 2016
Beginning Balance					$ 8,765		$ 8,162	$ 8,162
Charge-offs					(453)			(3,784)
Recoveries					510			150
Provision		$ 503		$ 247	1,451		1,907	4,237
Ending Balance		10,273			10,273			8,765
Allowance for credit losses, individually evaluated for impairment		373			373			536
Allowance for credit losses, collectively evaluated for impairment		9,900			9,900			8,195
Allowance for credit losses, purchased credit impaired	[1]							34
Loans receivable		1,297,959			1,297,959			975,284
Loans receivable, individually evaluated for impairment		12,505			12,505			13,449
Loans receivable, collectively evaluated for impairment		1,280,084			1,280,084			961,139
Loans receivable, purchased credit impaired		5,370	[1]		5,370	[1]		696	[1]	$ 1,776
Commercial Real Estate Portfolio Segment [Member] | Construction and Land [Member]
Beginning Balance					1,421		933	933
Charge-offs					(90)			(2)
Recoveries					398			1
Provision					(95)			489
Ending Balance		1,634			1,634			1,421
Allowance for credit losses, individually evaluated for impairment		0			0			36
Allowance for credit losses, collectively evaluated for impairment		1,634			1,634			1,385
Allowance for credit losses, purchased credit impaired	[1]	0			0			0
Loans receivable		196,404			196,404			143,535
Loans receivable, individually evaluated for impairment		7			7			92
Loans receivable, collectively evaluated for impairment		196,397			196,397			143,443
Loans receivable, purchased credit impaired	[1]	0			0			0
Commercial Real Estate Portfolio Segment [Member] | Farmland [Member]
Beginning Balance					76		75	75
Charge-offs					0			0
Recoveries					0			0
Provision					26			1
Ending Balance		102			102			76
Allowance for credit losses, individually evaluated for impairment		0			0			0
Allowance for credit losses, collectively evaluated for impairment		102			102			76
Allowance for credit losses, purchased credit impaired	[1]	0			0			0
Loans receivable		26,882			26,882			10,480
Loans receivable, individually evaluated for impairment		0			0			0
Loans receivable, collectively evaluated for impairment		26,882			26,882			10,480
Loans receivable, purchased credit impaired	[1]	0			0			0
Commercial Real Estate Portfolio Segment [Member] | Nonfarm Nonresidential [Member]
Beginning Balance					2,323		2,314	2,314
Charge-offs					0			(617)
Recoveries					13			23
Provision					236			603
Ending Balance		2,572			2,572			2,323
Allowance for credit losses, individually evaluated for impairment		54			54			46
Allowance for credit losses, collectively evaluated for impairment		2,518			2,518			2,277
Allowance for credit losses, purchased credit impaired	[1]	0			0			0
Loans receivable		432,306			432,306			337,699
Loans receivable, individually evaluated for impairment		4,123			4,123			5,831
Loans receivable, collectively evaluated for impairment		422,980			422,980			331,380
Loans receivable, purchased credit impaired	[1]	5,203			5,203			488
Residential Portfolio Segment [Member] | Real Estate Residential One- to Four-Family [Member]
Beginning Balance					1,284		1,228	1,228
Charge-offs					(290)			(184)
Recoveries					11			48
Provision					528			192
Ending Balance		1,533			1,533			1,284
Allowance for credit losses, individually evaluated for impairment		105			105			125
Allowance for credit losses, collectively evaluated for impairment		1,428			1,428			1,125
Allowance for credit losses, purchased credit impaired	[1]							34
Loans receivable		234,690			234,690			157,505
Loans receivable, individually evaluated for impairment		2,895			2,895			2,817
Loans receivable, collectively evaluated for impairment		231,628			231,628			154,480
Loans receivable, purchased credit impaired	[1]	167			167			208
Residential Portfolio Segment [Member] | Multi-family Residential [Member]
Beginning Balance					144		172	172
Charge-offs					0			0
Recoveries					0			0
Provision					1			(28)
Ending Balance		145			145			144
Allowance for credit losses, individually evaluated for impairment		0			0			0
Allowance for credit losses, collectively evaluated for impairment		145			145			144
Allowance for credit losses, purchased credit impaired	[1]	0			0			0
Loans receivable		22,109			22,109			20,717
Loans receivable, individually evaluated for impairment		0			0			0
Loans receivable, collectively evaluated for impairment		22,109			22,109			20,717
Loans receivable, purchased credit impaired	[1]	0			0			0
Commercial Portfolio Segment [Member]
Beginning Balance					3,147		3,039	3,039
Charge-offs					0			(2,945)
Recoveries					25			40
Provision					668			3,013
Ending Balance		3,840			3,840			3,147
Allowance for credit losses, individually evaluated for impairment		214			214			329
Allowance for credit losses, collectively evaluated for impairment		3,626			3,626			2,818
Allowance for credit losses, purchased credit impaired	[1]	0			0			0
Loans receivable		317,889			317,889			254,427
Loans receivable, individually evaluated for impairment		5,377			5,377			4,268
Loans receivable, collectively evaluated for impairment		312,512			312,512			250,159
Loans receivable, purchased credit impaired	[1]	0			0			0
Consumer Portfolio Segment [Member]
Beginning Balance					370		$ 401	401
Charge-offs					(73)			(36)
Recoveries					63			38
Provision					87			(33)
Ending Balance		447			447			370
Allowance for credit losses, individually evaluated for impairment		0			0			0
Allowance for credit losses, collectively evaluated for impairment		447			447			370
Allowance for credit losses, purchased credit impaired	[1]	0			0			0
Loans receivable		67,679			67,679			50,921
Loans receivable, individually evaluated for impairment		103			103			441
Loans receivable, collectively evaluated for impairment		67,576			67,576			50,480
Loans receivable, purchased credit impaired	[1]	$ 0			$ 0			$ 0

[1] Purchased credit impaired loans are evaluated for impairment on an individual basis.