Note 25 - Segments - Financial Information by Business Segment (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net interest income	$ 27,023	$ 26,164	$ 25,232	$ 25,184	$ 25,075	$ 24,760	$ 23,950	$ 23,469	$ 22,822	$ 22,081	$ 21,801	$ 21,614	$ 103,603	$ 97,254	$ 88,318
Provision (credit) for loan losses	900	150	600	900	500	1,250	750	500	750				2,550	3,000	750
Investment management and trust services													20,505	19,155	18,026
All other non-interest income													24,615	24,382	21,924
Non-interest expense	27,180	21,317	21,346	21,148	21,269	20,518	20,193	19,540	18,322	18,430	18,867	17,779	90,991	81,520	73,398
Income before income taxes	10,488	15,800	14,961	13,933	14,625	14,350	13,785	13,511	13,823	13,636	13,153	13,508	55,182	56,271	54,120
Income tax expense	5,542	$ 4,096	$ 4,359	$ 3,142	4,009	$ 3,883	$ 3,676	$ 3,676	4,177	$ 4,352	$ 4,151	$ 4,253	17,139	15,244	16,933
Net income													38,043	41,027	37,187
Segment assets	3,239,646				3,039,481				2,816,801				3,239,646	3,039,481	2,816,801
Commercial Banking [Member]
Net interest income													103,302	96,986	88,124
Provision (credit) for loan losses													2,550	3,000	750
Investment management and trust services
All other non-interest income													24,615	24,382	21,924
Non-interest expense													78,752	70,230	62,748
Income before income taxes													46,615	48,138	46,550
Income tax expense													14,080	12,340	14,238
Net income													32,535	35,798	32,312
Segment assets	3,237,656				3,037,394				2,816,373				3,237,656	3,037,394	2,816,373
Investment Management and Trust [Member]
Net interest income													301	268	194
Provision (credit) for loan losses
Investment management and trust services													20,505	19,155	18,026
All other non-interest income
Non-interest expense													12,239	11,290	10,650
Income before income taxes													8,567	8,133	7,570
Income tax expense													3,059	2,904	2,695
Net income													5,508	5,229	4,875
Segment assets	$ 1,990				$ 2,087				$ 428				$ 1,990	$ 2,087	$ 428