DERIVATIVES - Summary of Derivative Financial Instruments and Balances (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Inerest-bearing deposit liability	$ 2,358,312	$ 1,674,080
Derivative Asset	27,567	12,682
Estimate Fair Value Loss	(27,565)	(12,687)
Other Credit Derivatives [Member]
Derivatives, Fair Value [Line Items]
Inerest-bearing deposit liability	35,600	15,400
Credit Risk Derivative Liabilities, at Fair Value		100
Fair Value Hedges | Matched interest rate swaps | Accrued interest and other liabilities
Derivatives, Fair Value [Line Items]
Inerest-bearing deposit liability	1,179,156	837,040
Derivative Asset	24,306	5,529
Estimate Fair Value Loss	(3,259)	(7,158)
Fair Value Hedges | Matched interest rate swaps | Accrued interest and other assets
Derivatives, Fair Value [Line Items]
Inerest-bearing deposit liability	1,179,156	837,040
Derivative Asset	3,261	7,153
Estimate Fair Value Loss	$ (24,306)	$ (5,529)