QUARTERLY FINANCIAL DATA (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	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, 2016	Dec. 31, 2015	Dec. 31, 2014
Selected Income Statement Data
Interest income	$ 62,956	$ 62,210	$ 59,340	$ 54,559	$ 52,601	$ 51,195	$ 44,229	$ 42,368	$ 239,065	$ 190,393	$ 164,566
Interest expense	5,677	5,143	4,751	4,123	3,983	3,796	3,541	3,536	19,694	14,856	14,680
Net interest income	57,279	57,067	54,589	50,436	48,618	47,399	40,688	38,832	219,371	175,537	149,886
Provision for loan losses	1,710	811	889	681	553	986	2,656	1,069	4,091	5,264	5,648
Net interest income after provision for loan losses	55,569	56,256	53,700	49,755	48,065	46,413	38,032	37,763	215,280	170,273	144,238
Noninterest income	24,272	28,864	28,379	24,286	22,407	24,978	20,626	17,575	105,801	85,586	62,836
Noninterest expense	54,660	53,199	52,359	49,241	51,221	47,950	51,152	40,812	215,835	199,115	150,869
Merger and conversion charges	17	0	0	6,359	1,807	446	5,712	15
Income before income taxes	25,164	31,921	29,720	18,441	17,444	22,995	1,794	14,511	105,246	56,744	56,205
Income tax	6,987	10,364	9,671	6,124	3,296	7,368	486	4,747	33,146	15,897	17,482
Net income	$ 18,177	$ 21,557	$ 20,049	$ 12,317	$ 14,148	$ 15,627	$ 1,308	$ 9,764	$ 72,100	$ 40,847	$ 38,723
Per Share Data
Net income - basic	$ 0.52	$ 0.62	$ 0.58	$ 0.38	$ 0.44	$ 0.49	$ 0.04	$ 0.32	$ 2.10	$ 1.29	$ 1.48
Net income - diluted	0.52	0.61	0.57	0.37	0.43	0.48	0.04	0.32	$ 2.08	$ 1.27	$ 1.46
Common dividends - cash	$ 0.10	$ 0.10	$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 0.05