FAIR VALUE DISCLOSURES OF FINANCIAL ASSETS AND LIABILITIES - Schedule of Financial Instruments Carried at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 1,523,196	$ 1,205,079
Investment securities available for sale	1,523,196	1,205,079
Total assets measured at fair value on a nonrecurring basis		112,313
Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	1,527,216	1,207,177
Investment securities available for sale	1,527,216	1,207,177
Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	129,900
CMO
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	395,180	371,750
Investment securities available for sale	395,180	371,750
CMO | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	395,180	371,750
Investment securities available for sale	395,180	371,750
FNMA MBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	877,773	644,073
Investment securities available for sale	877,773	644,073
FNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	877,773	644,073
Investment securities available for sale	877,773	644,073
FHLMC MBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	214,932	153,922
Investment securities available for sale	214,932	153,922
FHLMC MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	214,932	153,922
Investment securities available for sale	214,932	153,922
GNMA MBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	35,311	35,334
Investment securities available for sale	35,311	35,334
GNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	35,311	35,334
Investment securities available for sale	35,311	35,334
Other Assets | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	4,020	2,098
Investment securities available for sale	4,020	2,098
Other Liabilities | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other liabilities	5,315	3,493
Other equity investments | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	48,450	37,233
Other real estate owned | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	2,233	2,668
Loans held for sale | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	33,893	25,318
Impaired loans, net | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	45,324	47,094
Quoted Prices in Active Markets for Identical Asset (Level 1)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis		0
Quoted Prices in Active Markets for Identical Asset (Level 1) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	0	0
Investment securities available for sale	0	0
Quoted Prices in Active Markets for Identical Asset (Level 1) | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	0
Quoted Prices in Active Markets for Identical Asset (Level 1) | CMO | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	0	0
Investment securities available for sale	0	0
Quoted Prices in Active Markets for Identical Asset (Level 1) | FNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	0	0
Investment securities available for sale	0	0
Quoted Prices in Active Markets for Identical Asset (Level 1) | FHLMC MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	0	0
Investment securities available for sale	0	0
Quoted Prices in Active Markets for Identical Asset (Level 1) | GNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	0	0
Investment securities available for sale	0	0
Quoted Prices in Active Markets for Identical Asset (Level 1) | Other Assets | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	0	0
Investment securities available for sale	0	0
Quoted Prices in Active Markets for Identical Asset (Level 1) | Other Liabilities | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other liabilities	0	0
Quoted Prices in Active Markets for Identical Asset (Level 1) | Other equity investments | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	0	0
Quoted Prices in Active Markets for Identical Asset (Level 1) | Other real estate owned | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	0	0
Quoted Prices in Active Markets for Identical Asset (Level 1) | Loans held for sale | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	0	0
Quoted Prices in Active Markets for Identical Asset (Level 1) | Impaired loans, net | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	0	0
Significant Other Observable Inputs (Level 2)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis		25,318
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	1,527,216	1,207,177
Investment securities available for sale	1,527,216	1,207,177
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	33,893
Significant Other Observable Inputs (Level 2) | CMO | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	395,180	371,750
Investment securities available for sale	395,180	371,750
Significant Other Observable Inputs (Level 2) | FNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	877,773	644,073
Investment securities available for sale	877,773	644,073
Significant Other Observable Inputs (Level 2) | FHLMC MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	214,932	153,922
Investment securities available for sale	214,932	153,922
Significant Other Observable Inputs (Level 2) | GNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	35,311	35,334
Investment securities available for sale	35,311	35,334
Significant Other Observable Inputs (Level 2) | Other Assets | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	4,020	2,098
Investment securities available for sale	4,020	2,098
Significant Other Observable Inputs (Level 2) | Other Liabilities | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other liabilities	5,315	3,493
Significant Other Observable Inputs (Level 2) | Other equity investments | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	0	0
Significant Other Observable Inputs (Level 2) | Other real estate owned | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	0	0
Significant Other Observable Inputs (Level 2) | Loans held for sale | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	33,893	25,318
Significant Other Observable Inputs (Level 2) | Impaired loans, net | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	0	0
Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis		86,995
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	0	0
Investment securities available for sale	0	0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	96,007
Significant Unobservable Inputs (Level 3) | CMO | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	0	0
Investment securities available for sale	0	0
Significant Unobservable Inputs (Level 3) | FNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	0	0
Investment securities available for sale	0	0
Significant Unobservable Inputs (Level 3) | FHLMC MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	0	0
Investment securities available for sale	0	0
Significant Unobservable Inputs (Level 3) | GNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	0	0
Investment securities available for sale	0	0
Significant Unobservable Inputs (Level 3) | Other Assets | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	0	0
Investment securities available for sale	0	0
Significant Unobservable Inputs (Level 3) | Other Liabilities | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other liabilities	0	0
Significant Unobservable Inputs (Level 3) | Other equity investments | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	48,450	37,233
Significant Unobservable Inputs (Level 3) | Other real estate owned | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	2,233	2,668
Significant Unobservable Inputs (Level 3) | Loans held for sale | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	0	0
Significant Unobservable Inputs (Level 3) | Impaired loans, net | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value on a nonrecurring basis	$ 45,324	$ 47,094