COMMITMENTS AND CONTINGENT LIABILITIES - Schedule of Guarantor Obligations (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments to extend credit	$ 1,671,419	$ 1,109,806
Unused home equity lines of credit	112,310	69,788
Financial standby letters of credit	24,596	11,389
Mortgage interest rate lock commitments	81,833	86,149
Mortgage forward contracts with positive fair value	$ 0	$ 31,500