INCOME TAXES - Reconciliation Effective Income Tax Amount (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
Income Tax Disclosure [Abstract]
Federal income statutory rate									21.00%	21.00%	21.00%
Tax at federal income tax rate									$ 71,460	$ 44,433	$ 31,813
Change resulting from:
State income tax, net of federal benefit									9,812	7,389	1,965
Tax-exempt interest									(3,726)	(2,911)	(3,095)
Increase in cash value of bank owned life insurance									(594)	(581)	(382)
Excess tax (benefit) deficiency from stock compensation									371	(108)	(602)
Nondeductible merger expenses									2	799	1,002
Other									2,827	1,122	(238)
Benefit related to carryback claims resulting from the CARES Act									(1,896)	0	0
Provision for income taxes	$ 31,708	$ 34,037	$ 8,609	$ 3,902	$ 20,959	$ 5,692	$ 12,064	$ 11,428	$ 78,256	$ 50,143	$ 30,463