LOANS AND ALLOWANCE FOR LOAN LOSSES - Rollforward for Purchased Loans (Details) - Purchased Loans - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance, January 1	$ 2,588,832	$ 861,595
Charge-offs	(5,275)	(1,803)
Additions due to acquisitions	3,511,645	2,053,744
Accretion	20,255	11,918
Purchase of acquired formerly serviced portfolio	103,530	0
Subsequent fair value adjustments recorded to goodwill	(4,854)	0
Loans sold	(109,611)	0
Transfers to loans held for sale	(8,293)	0
Transfers to purchased other real estate owned	(5,135)	(6,396)
Payments received	(1,015,798)	(330,226)
Other	(15)	0
Ending balance	$ 5,075,281	$ 2,588,832