Note 23 - Quarterly Financial Data (Unaudited) - Quarterly Financial Data (Unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest income	$ 37,195,000	$ 35,486,000	$ 34,319,000	$ 34,981,000	$ 32,902,000	$ 33,034,000	$ 30,903,000	$ 28,704,000	$ 141,981,000	$ 125,543,000	$ 118,457,000
Net interest income	30,818,000	29,840,000	29,225,000	30,199,000	28,402,000	28,644,000	27,193,000	25,509,000	120,082,000	109,748,000	105,867,000
Net income	$ 11,574,000	$ 10,123,000	$ 9,446,000	$ 10,881,000	$ 7,979,000	$ 8,337,000	$ 7,343,000	$ 7,615,000	$ 42,024,000	$ 31,274,000	$ 31,913,000
Earnings per share basic (in dollars per share)	$ 0.70	$ 0.61	$ 0.57	$ 0.66	$ 0.48	$ 0.51	$ 0.45	$ 0.46	$ 2.53	$ 1.90	$ 1.96
Earnings per share diluted (in dollars per share)	$ 0.70	$ 0.61	$ 0.57	$ 0.66	$ 0.48	$ 0.51	$ 0.45	$ 0.46	$ 2.53	$ 1.90	$ 1.96