Note 5 - Credit Quality (Details Textual) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Percentage of Loan Loss Covered by FDIC		80.00%
Financing Receivable, Collectively Evaluated for Impairment		$ 1,758,011		$ 1,785,574
Loans Deemed to be Impaired, Threshold			$ 500	250
Impaired Financing Receivable, Recorded Investment, Total	[1]	33,008		33,301
Restructured Loans, Reserves		$ 250
Performing Status Returned Period		180 days
Financing Receivable, Modifications, Recorded Investment		$ 9,008		9,663
Financial Asset Acquired with Credit Deterioration [Member]
Impaired Financing Receivable, Recorded Investment, Total		0		0
Impaired Loans [Member]
Financing Receivable, Collectively Evaluated for Impairment		25,270		20,130
Non-covered Loans [Member]
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		58		1
Covered Loans [Member]
Financing Receivable, Modifications, Recorded Investment		$ 0		$ 0

[1] Total impaired loans include loans totaling $25.27 million as of December 31, 2018, and $20.13 million as of December 31, 2017, that do not meet the Company's evaluation threshold for individual impairment and are therefore collectively evaluated for impairment. During the first quarter of 2018, the Company changed the threshold for quarterly reviews of individual loans that are deemed to be impaired from $250 thousand to $500 thousand or greater.