SELECTED QUARTERLY DATA (UNAUDITED) - Summary Of Selected Quarterly Data (Details) - USD ($) $ / shares in Units, $ in Thousands	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
SELECTED QUARTERLY DATA (UNAUDITED)
Interest income	$ 52,312	$ 54,769	$ 54,635	$ 53,494	$ 53,728	$ 50,379	$ 48,795	$ 46,068	$ 215,210	$ 198,970	$ 165,698
Interest expense	13,430	15,224	16,224	15,285	14,138	12,454	11,262	9,845	60,163	47,699	29,806
Net interest income	38,882	39,545	38,411	38,209	39,590	37,925	37,533	36,223	155,047	151,271	135,892
Provision for loan losses	250	1,000	785	1,200	300	1,100	1,700	3,300	3,235	6,400	3,000
Net interest income after provision	38,632	38,545	37,626	37,009	39,290	36,825	35,833	32,923	151,812	144,871	132,892
Noninterest income	11,119	10,765	11,588	11,525	10,077	10,624	9,722	9,879
Noninterest expense	22,122	22,737	22,092	22,473	22,524	22,200	20,303	21,202	89,424	86,229	79,298
Income tax expense	5,431	5,119	5,409	4,379	5,480	4,679	5,110	3,264	20,338	18,533	32,304
Net income	$ 22,198	$ 21,454	$ 21,713	$ 21,682	$ 21,363	$ 20,570	$ 20,142	$ 18,336	$ 87,047	$ 80,411	$ 57,330
Basic earnings per common share	$ 0.86	$ 0.84	$ 0.85	$ 0.85	$ 0.84	$ 0.81	$ 0.80	$ 0.73	$ 3.40	$ 3.18	$ 2.28
Diluted earnings per common share	$ 0.86	$ 0.83	$ 0.85	$ 0.84	$ 0.83	$ 0.80	$ 0.79	$ 0.71	$ 3.38	$ 3.13	$ 2.23