GOODWILL AND OTHER INTANGIBLE ASSETS - Carrying Amount of Goodwill (Details) - USD ($)	3 Months Ended				9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Change in the carrying amount	$ 0	$ 0	$ 727,000	$ 2,341,000	$ 0
Goodwill [Roll Forward]
Goodwill - net book value, begging of period		1,428,610,000	1,427,883,000	1,425,542,000	1,428,610,000
Merger purchase accounting adjustments and changes	0	0	727,000	2,341,000	0
Goodwill - net book value, end of period	$ 1,428,610,000	$ 1,428,610,000	$ 1,428,610,000	$ 1,427,883,000	$ 1,428,610,000