DERIVATIVES - Summary of Derivative Financial Instruments and Balances (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Inerest-bearing deposit liability	$ 1,816,432	$ 1,674,080
Derivative Asset	16,325	12,682
Estimate Fair Value Loss	(16,327)	(12,687)
Other Credit Derivatives [Member]
Derivatives, Fair Value [Line Items]
Inerest-bearing deposit liability	10,100	15,400
Credit Risk Derivative Liabilities, at Fair Value	100	71
Fair Value Hedges | Matched interest rate swaps | Accrued interest and other liabilities
Derivatives, Fair Value [Line Items]
Inerest-bearing deposit liability	908,216	837,040
Derivative Asset	13,225	5,529
Estimate Fair Value Loss	(3,102)	(7,158)
Fair Value Hedges | Matched interest rate swaps | Accrued interest and other assets
Derivatives, Fair Value [Line Items]
Inerest-bearing deposit liability	908,216	837,040
Derivative Asset	3,100	7,153
Estimate Fair Value Loss	$ (13,225)	$ (5,529)