FAIR VALUE MEASURES - Significant Unobservable Inputs Used in Fair Value Measurement of Level 3 Assets and Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Recurring assets at fair value	$ 960,821	$ 932,973
Nonrecurring assets at fair value	39,171	41,965
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	39,171	41,965
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	$ 28,790	$ 28,253
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	100.00%	100.00%
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	25.00%	28.00%
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	10.00%	15.00%
Other real estate owned
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	$ 435	$ 1,172
Other real estate owned | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	435	1,172
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	$ 435	$ 1,172
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	20.00%	74.00%
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	13.00%	22.00%
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	$ 9,946	$ 12,540
Purchased other real estate owned | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	9,946	12,540
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	$ 9,946	$ 12,540
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	16.00%	15.00%
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%