FAIR VALUE MEASURES - Significant Unobservable Inputs Used in Fair Value Measurement of Level 3 Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Recurring assets at fair value	$ 964,686	$ 1,011,203
Nonrecurring assets at fair value	33,564	37,018
Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Recurring assets at fair value	1,500	1,500
Nonrecurring assets at fair value	33,564	37,018
Fair Value, Measurements, Recurring | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Recurring assets at fair value	$ 1,500	$ 1,500
Valuation Technique	Discounted par values	Discounted par values
Unobservable Inputs	Credit quality of underlying issuer	Credit quality of underlying issuer
Fair value inputs discount rate range	0.00%	0.00%
Fair Value, Measurements, Recurring | Weighted Average Daily Balance | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	0.00%	0.00%
Impaired loans | Fair Value, Measurements, Nonrecurring | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	$ 26,133	$ 27,684
Valuation Technique	Third-party appraisals and discounted cash flows	Third-party appraisals and discounted cash flows
Unobservable Inputs	Collateral discounts and discount rates	Collateral discounts and discount rates
Impaired loans | Fair Value, Measurements, Nonrecurring | Maximum | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	90.00%	90.00%
Impaired loans | Fair Value, Measurements, Nonrecurring | Weighted Average Daily Balance | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	27.00%	24.00%
Impaired loans | Fair Value, Measurements, Nonrecurring | Minimum | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	15.00%	20.00%
Other real estate owned
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	$ 708	$ 323
Other real estate owned | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	708	323
Other real estate owned | Fair Value, Measurements, Nonrecurring | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	$ 708	$ 323
Valuation Technique	Third-party appraisals and sales contracts	Third-party appraisals and sales contracts
Unobservable Inputs	Collateral discounts and estimated costs to sell	Collateral discounts and estimated costs to sell
Other real estate owned | Fair Value, Measurements, Nonrecurring | Maximum | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	32.00%	15.00%
Other real estate owned | Fair Value, Measurements, Nonrecurring | Weighted Average Daily Balance | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	17.00%	15.00%
Other real estate owned | Fair Value, Measurements, Nonrecurring | Minimum | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	15.00%	15.00%
Purchased other real estate owned
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	$ 6,723	$ 9,011
Purchased other real estate owned | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	6,723	9,011
Purchased other real estate owned | Fair Value, Measurements, Nonrecurring | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	$ 6,723	$ 9,011
Valuation Technique	Third-party appraisals	Third-party appraisals
Unobservable Inputs	Collateral discounts and estimated costs to sell	Collateral discounts and estimated costs to sell
Purchased other real estate owned | Fair Value, Measurements, Nonrecurring | Maximum | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	74.00%	74.00%
Purchased other real estate owned | Fair Value, Measurements, Nonrecurring | Weighted Average Daily Balance | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	17.00%	26.00%
Purchased other real estate owned | Fair Value, Measurements, Nonrecurring | Minimum | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	10.00%	10.00%