COMMITMENTS AND CONTINGENCIES - Schedule of Guarantor Obligations (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments to extend credit	$ 2,403,565	$ 1,671,419
Unused home equity lines of credit	267,503	112,310
Financial standby letters of credit	30,308	24,596
Mortgage interest rate lock commitments	$ 603,518	$ 81,833