DERIVATIVES - Summary of Derivative Financial Instruments and Balances (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Inerest-bearing deposit liability	$ 2,813,828	$ 2,719,980
Derivative Asset	38,801	29,189
Estimate Fair Value Loss	(38,808)	(29,188)
Other Credit Derivatives [Member]
Derivatives, Fair Value [Line Items]
Inerest-bearing deposit liability	32,800	12,300
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	1,406,914	1,359,990
Derivative Asset	5,580	11,787
Estimate Fair Value Loss	(33,228)	(17,401)
Fair Value Hedges | Matched interest rate swaps | Accrued interest and other assets
Derivatives, Fair Value [Line Items]
Inerest-bearing deposit liability	1,406,914	1,359,990
Derivative Asset	33,221	17,402
Estimate Fair Value Loss	$ (5,580)	$ (11,787)