Note 5 - Credit Quality (Details Textual) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Collectively Evaluated for Impairment		$ 1,672,634	$ 1,755,339
Loans Deemed to be Impaired, Threshold				$ 500	$ 250
Impaired Financing Receivable, Recorded Investment, Total	[1]	31,172	33,008
Restructured Loans, Reserves		$ 250
Performing Status Returned Period		180 days
Financing Receivable, Troubled Debt Restructuring		$ 8,917	9,008
Financial Asset Acquired with Credit Deterioration [Member]
Impaired Financing Receivable, Recorded Investment, Total		0	0
Impaired Loans [Member]
Financing Receivable, Collectively Evaluated for Impairment		24,640	25,270
Non-covered Loans [Member]
Financing Receivable, 90 Days or More Past Due, Still Accruing		144	58
Covered Loans [Member]
Financing Receivable, Troubled Debt Restructuring		$ 0	$ 0

[1] Total impaired loans include loans totaling $24.35 million as of December 31, 2019, and $25.27 million as of December 31, 2018, 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.