COMMITMENTS AND CONTINGENT LIABILITIES - Schedule of Guarantor Obligations (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments to extend credit	$ 1,109,806	$ 1,101,257
Unused home equity lines of credit	69,788	62,586
Financial standby letters of credit	11,389	14,257
Mortgage interest rate lock commitments	86,149	91,426
Mortgage forward contracts with positive fair value	$ 31,500	$ 150,000