COMMITMENTS AND CONTINGENCIES - Schedule of Guarantor Obligations (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments to extend credit	$ 1,527,944	$ 1,109,806
Unused home equity lines of credit	109,417	69,788
Financial standby letters of credit	16,397	11,389
Mortgage interest rate lock commitments	153,544	86,149
Mortgage forward contracts with positive fair value	$ 0	$ 31,500