FAIR VALUE DISCLOSURES - Summary of Financial Assets and Liabilities Measure at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets
Derivatives	$ 38,801	$ 29,189
Investment securities available-for-sale	3,113,811	2,779,255
Liabilities
Derivatives	38,808	29,188
Fair Value, Measurements, Recurring
Assets
Derivatives	39,062	29,543
Investment securities available-for-sale	3,113,811	2,779,255
Total	3,152,873	2,808,798
Liabilities
Derivatives	38,985	29,336
Fair Value, Measurements, Recurring \| Fair Value Measurements Using Level 1
Assets
Derivatives	0	0
Investment securities available-for-sale	98	97
Total	98	97
Liabilities
Derivatives	0	0
Fair Value, Measurements, Recurring \| Fair Value Measurements Using Level 2
Assets
Derivatives	39,062	29,543
Investment securities available-for-sale	3,100,358	2,764,443
Total	3,139,420	2,793,986
Liabilities
Derivatives	38,985	29,336
Fair Value, Measurements, Recurring \| Fair Value Measurements Using Level 3
Assets
Derivatives	0	0
Investment securities available-for-sale	13,355	14,715
Total	13,355	14,715
Liabilities
Derivatives	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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