SUMMARY OF QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	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, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Net interest income	$ 132,575	$ 122,497	$ 124,146	$ 112,511	$ 112,745	$ 111,321	$ 106,708	$ 102,955	$ 491,729	$ 433,729	$ 413,954
Provision for credit losses	17,072	1,678	26,796	21,520	4,903	5,201	4,918	1,635	67,066	16,657	24,013
NET INTEREST INCOME AFTER PROVISION FOR CREDIT LOSSES	115,503	120,819	97,350	90,991	107,842	106,120	101,790	101,320	424,663	417,072	389,941
Noninterest income	32,621	31,216	30,637	25,817	28,030	29,400	32,061	26,717	120,291	116,208	109,160
Noninterest expense	99,269	90,396	90,439	90,859	92,866	92,967	75,098	88,230	370,963	349,161	353,888
Income taxes	9,046	13,681	7,417	5,909	5,155	7,941	13,584	8,310	36,053	34,990	28,215
NET INCOME	39,809	47,958	30,131	20,040	37,851	34,612	45,169	31,497	137,938	149,129	116,998
Preferred dividends	(2,014)	(2,437)	0	0	0	0	0	0	(4,451)	0	(39)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS	$ 37,795	$ 45,521	$ 30,131	$ 20,040	$ 37,851	$ 34,612	$ 45,169	$ 31,497	$ 133,487	$ 149,129	$ 116,959
Per share:
Earnings per share — basic (in dollars per share)	$ 0.98	$ 1.23	$ 0.82	$ 0.54	$ 1.03	$ 0.94	$ 1.26	$ 0.91	$ 3.58	$ 4.14	$ 3.54
Earnings per share — diluted (in dollars per share)	0.98	1.23	0.82	0.54	1.03	0.94	1.26	0.91	3.57	4.14	3.52
Cash dividends declared on common stock (in dollars per share)	0.20	0.20	0.20	0.20	0.18	0.18	0.16	0.16	$ 0.80	$ 0.68	$ 0.59
Book value per common share (in dollars per share)	$ 46.77	$ 46.11	$ 44.42	$ 42.21	$ 43.00	$ 42.62	$ 41.48	$ 39.65
Weighted average common shares outstanding (in shares)	38,420,063	36,941,110	36,880,325	36,820,972	36,758,025	36,692,381	35,743,986	34,564,378	37,269,000	35,991,000	33,012,000
Weighted average diluted common shares outstanding (in shares)	38,534,082	36,995,572	36,915,630	36,895,591	36,840,519	36,835,191	35,879,259	34,699,839	37,357,000	36,062,000	33,213,000