COMMITMENTS AND CONTINGENCIES - Schedule of Guarantor Obligations (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments to extend credit	$ 3,193,867	$ 2,826,719
Unused home equity lines of credit	257,967	259,015
Financial standby letters of credit	31,359	33,613
Mortgage interest rate lock commitments	$ 1,033,336	$ 1,199,939