FAIR VALUE DISCLOSURES OF FINANCIAL ASSETS AND LIABILITIES - Schedule of Financial Instruments Carried at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	$ 2,334,922	$ 1,944,914
Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other assets	18,448	4,884
Other liabilities	33,555	3,918
Total assets	2,353,370	1,949,798
Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other real estate owned	3,000	2,605
Total assets	165,889	156,523
CMO
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	428,533	340,230
CMO | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	428,533	340,230
FNMA MBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	1,454,908	1,242,453
FNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	1,454,908	1,242,453
FHLMC MBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	246,224	328,946
FHLMC MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	246,224	328,946
GNMA MBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	26,630	33,285
GNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	26,630	33,285
GSE agency notes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	178,627
GSE agency notes | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	178,627
Other investments | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	10,436	70,046
Loans held for sale | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale	152,453	83,872
Quoted Prices in Active Markets for Identical Asset (Level 1) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other assets	0	0
Other liabilities	0	0
Total assets	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]
Other real estate owned	0	0
Total assets	0	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]
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]
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]
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]
Investment securities available-for-sale	0	0
Quoted Prices in Active Markets for Identical Asset (Level 1) | GSE agency notes | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	0
Quoted Prices in Active Markets for Identical Asset (Level 1) | Other investments | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	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]
Loans held-for-sale	0	0
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other assets	18,448	4,884
Other liabilities	8,350	3,918
Total assets	2,353,370	1,949,798
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other real estate owned	0	0
Total assets	152,453	83,872
Significant Other Observable Inputs (Level 2) | CMO | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	428,533	340,230
Significant Other Observable Inputs (Level 2) | FNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	1,454,908	1,242,453
Significant Other Observable Inputs (Level 2) | FHLMC MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	246,224	328,946
Significant Other Observable Inputs (Level 2) | GNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	26,630	33,285
Significant Other Observable Inputs (Level 2) | GSE agency notes | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	178,627
Significant Other Observable Inputs (Level 2) | Other investments | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	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]
Loans held-for-sale	152,453	83,872
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other assets	0	0
Other liabilities	25,205	0
Total assets	0	0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other real estate owned	3,000	2,605
Total assets	13,436	72,651
Significant Unobservable Inputs (Level 3) | CMO | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
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]
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]
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]
Investment securities available-for-sale	0	0
Significant Unobservable Inputs (Level 3) | GSE agency notes | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale	0
Significant Unobservable Inputs (Level 3) | Other investments | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	10,436	70,046
Significant Unobservable Inputs (Level 3) | Loans held for sale | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale	$ 0	$ 0