Note 19 - Quarterly Financial Information - Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Interest and loan fee income	$ 43,041	$ 43,810	$ 44,276	$ 42,316	$ 42,961	$ 41,365	$ 41,539	$ 39,991	$ 39,878	$ 39,695	$ 39,626	$ 39,483	$ 173,443	$ 165,856	$ 158,682
Net interest income	42,537	43,318	43,792	41,841	42,480	40,899	41,104	39,549	39,427	39,240	39,139	38,989	171,488	164,032	156,794
Provision for loan losses	0	0	0	0	0	0	0	4,300	0	0	0	0
Noninterest income	10,842	11,282	11,032	10,189	13,959	10,476	9,554	11,648	11,732	11,809	12,288	11,579	43,345	45,637	47,408
Noninterest expense	23,912	24,697	24,291	24,906	24,545	24,603	24,754	24,664	24,209	24,033	25,561	25,183	97,806	98,566	98,986
Income before taxes and equity in undistributed income of subsidiaries	29,467	29,903	30,533	27,124	31,894	26,772	25,904	22,233	26,950	27,016	25,866	25,385	117,027	106,803	105,216
Net income	$ 21,720	$ 22,063	$ 22,579	$ 20,147	$ 23,838	$ 20,051	$ 19,562	$ 16,962	$ 20,728	$ 20,390	$ 19,625	$ 19,646	$ 86,509	$ 80,413	$ 80,389
Basic earnings per common share (in dollars per share)	$ 0.81	$ 0.82	$ 0.84	$ 0.75	$ 0.89	$ 0.74	$ 0.72	$ 0.63	$ 0.77	$ 0.76	$ 0.73	$ 0.73	$ 3.22	$ 2.98	$ 2.98
Diluted earnings per common share (in dollars per share)	0.81	0.82	0.84	0.75	0.89	0.74	0.72	0.63	0.77	0.75	0.73	0.73	3.22	2.98	2.98
Dividends paid per common share (in dollars per share)	0.42	0.41	0.41	0.41	0.41	0.41	0.41	0.41	0.41	0.41	0.41	0.40	1.65	1.64	1.63
Share price, common stock (in dollars per share)	57.73												57.73
Minimum [Member]
Share price, common stock (in dollars per share)	53.78	54.03	57.67	55.82	51.49	51.84	53.40	47.37	60.65	59.26	59.51	56.82	53.78	51.49	60.65
Maximum [Member]
Share price, common stock (in dollars per share)	$ 58.00	$ 58.55	$ 64.80	$ 66.43	$ 59.70	$ 63.58	$ 64.86	$ 68.01	$ 68.58	$ 64.56	$ 64.82	$ 64.48	$ 58.00	$ 59.70	$ 68.58