Note 22 - Quarterly Financial Data (Unaudited) - Quarterly Financial Data (Unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest income	$ 39,564,000	$ 40,316,000	$ 39,820,000	$ 38,637,000	$ 37,195,000	$ 35,486,000	$ 34,319,000	$ 34,981,000	$ 158,337,000	$ 141,981,000	$ 125,543,000
Net interest income	31,168,000	31,605,000	31,116,000	30,645,000	30,818,000	29,840,000	29,225,000	30,199,000	124,534,000	120,082,000	109,748,000
Net income	$ 13,317,000	$ 12,600,000	$ 11,715,000	$ 11,824,000	$ 11,574,000	$ 10,123,000	$ 9,446,000	$ 10,881,000	$ 49,456,000	$ 42,024,000	$ 31,274,000
Earnings per share basic (in dollars per share)	$ 0.81	$ 0.77	$ 0.71	$ 0.72	$ 0.70	$ 0.61	$ 0.57	$ 0.66	$ 3.01	$ 2.53	$ 1.90
Earnings per share diluted (in dollars per share)	$ 0.81	$ 0.77	$ 0.71	$ 0.72	$ 0.70	$ 0.61	$ 0.57	$ 0.66	$ 3.01	$ 2.53	$ 1.90