PARENT COMPANY ONLY FINANCIAL INFORMATION (Income Statements) (Details) - USD ($) $ 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
Operating expenses:
Interest									$ 44,883	$ 80,600	$ 51,866
Salaries and employee benefits									202,668	200,341	195,362
Professional fees									54,068	47,697	41,414
INCOME BEFORE INCOME TAXES									173,991	184,119	145,213
Income tax benefit	$ (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
Parent
Operating revenues:
Dividends from subsidiaries									83,000	137,000	85,000
Other									1,948	893	493
Total operating revenues									84,948	137,893	85,493
Operating expenses:
Interest									13,573	15,044	14,371
Salaries and employee benefits									8,147	4,072	3,639
Professional fees									4,310	3,029	2,841
Other operating expenses									4,939	15,559	12,510
Total operating expenses									30,969	37,704	33,361
Equity in undistributed earnings									73,430	34,307	52,570
INCOME BEFORE INCOME TAXES									127,409	134,496	104,702
Income tax benefit									10,529	14,633	12,296
NET INCOME									137,938	149,129	116,998
Preferred dividends									(4,451)	0	(39)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS									$ 133,487	$ 149,129	$ 116,959