COMMITMENTS AND CONTINGENCIES - Schedule of Guarantor Obligations (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments to extend credit	$ 2,340,433	$ 2,486,949
Unused home equity lines of credit	259,421	262,089
Financial standby letters of credit	33,087	29,232
Mortgage interest rate lock commitments	$ 1,658,214	$ 288,490