Note 1 - Nature of Operations - Summary of Significant Accounting Policies - (Details Textual) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Nov. 30, 2018	Jan. 01, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets, Total			$ 2,094,896	$ 1,321,256
Loans and Leases Receivable, Net of Deferred Income, Total			1,528,469	975,284
Deposits, Total			1,733,934	1,055,533
Stockholders' Equity Attributable to Parent, Ending Balance			260,058	179,935	$ 113,559	$ 112,449
Debt Securities, Held-to-maturity, Total			0	0
Debt Securities, Trading, and Equity Securities, FV-NI, Total			0	0
Real Estate Acquired Through Foreclosure			1,909	227
Advertising Expense			$ 1,200	1,200	$ 1,300
Core Deposits [Member]
Finite-Lived Intangible Asset, Useful Life			10 years
Residential Real Estate [Member]
Real Estate Acquired Through Foreclosure			$ 0	0
Minden Bancorp [Member]
Assets, Total				317,400
Loans and Leases Receivable, Net of Deferred Income, Total				192,700
Deposits, Total				264,000
Stockholders' Equity Attributable to Parent, Ending Balance				$ 30,600
Richland State Bancorp [Member]
Assets, Total	$ 316,500
Loans and Leases Receivable, Net of Deferred Income, Total	191,000
Deposits, Total	290,000
Stockholders' Equity Attributable to Parent, Ending Balance	$ 25,400
Minden Bancorp [Member]
Payments to Acquire Businesses, Gross		$ 56,187
Business Acquisition, Price Paid Per Share of Common Stock of Acquired Entity		$ 23.20
Richland State Bancorp [Member]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	1,679,559
Business Combination, Consideration Transferred, Total	$ 42,476