FAIR VALUE MEASUREMENTS - Unobservable Inputs Recurring (Details) $ in Thousands	Sep. 30, 2020 USD ($) uSDPerLoan	Dec. 31, 2019 USD ($) uSDPerLoan
Quantitative information about the significant unobservable inputs within Level 3
Trading security	$ 9,525	$ 10,769
Securities available for sale, at fair value	1,575,289	1,311,555
Level 3
Quantitative information about the significant unobservable inputs within Level 3
Securities available for sale, at fair value	25,825	43,982
Level 3 | Recurring
Quantitative information about the significant unobservable inputs within Level 3
Trading security	9,525	10,769
Securities available for sale, at fair value	25,825	42,966
Loan held for investment	2,774
Total	$ 43,874	$ 68,662
Level 3 | Recurring | Discounted Cash Flow | Discount rate
Quantitative information about the significant unobservable inputs within Level 3
Trading security, significant unobservable input value	0.0375	0.0221
Loan held for investment, measurement input	0.3000
Level 3 | Recurring | Forward commitments
Quantitative information about the significant unobservable inputs within Level 3
Derivative asset	$ 397
Level 3 | Recurring | Forward commitments | Historical Trend | Closing Ratio
Quantitative information about the significant unobservable inputs within Level 3
Derivative asset, significant unobservable input value	0.7440
Level 3 | Recurring | Forward commitments | Pricing Model | Origination Costs, per loan
Quantitative information about the significant unobservable inputs within Level 3
Derivative asset, significant unobservable input value | uSDPerLoan	3,000
Level 3 | Recurring | Commitments to lend
Quantitative information about the significant unobservable inputs within Level 3
Derivative asset	$ 1,498	$ 2,628
Level 3 | Recurring | Commitments to lend | Historical Trend | Closing Ratio
Quantitative information about the significant unobservable inputs within Level 3
Derivative asset, significant unobservable input value	0.7440	0.7781
Level 3 | Recurring | Commitments to lend | Pricing Model | Origination Costs, per loan
Quantitative information about the significant unobservable inputs within Level 3
Derivative asset, significant unobservable input value | uSDPerLoan	3,000	3,000
Level 3 | Recurring | Capitalized servicing rights
Quantitative information about the significant unobservable inputs within Level 3
Capitalized servicing rights	$ 3,855	$ 12,299
Level 3 | Recurring | Capitalized servicing rights | Discounted Cash Flow | Discount rate
Quantitative information about the significant unobservable inputs within Level 3
Servicing asset, significant unobservable input value	0.1000	0.1000
Level 3 | Recurring | Capitalized servicing rights | Discounted Cash Flow | Constant prepayment rate (CPR)
Quantitative information about the significant unobservable inputs within Level 3
Servicing asset, significant unobservable input value	0.2535	0.1150
Minimum | Level 3 | Recurring | Discounted Cash Flow | Collateral Value
Quantitative information about the significant unobservable inputs within Level 3
Loan held for investment, measurement input	8,800,000
Minimum | AFS Securities | Level 3 | Recurring | Indication from Market Maker | Price
Quantitative information about the significant unobservable inputs within Level 3
Debt securities, available-for-sale, measurement input	0.97	0.97
Maximum | Level 3 | Recurring | Discounted Cash Flow | Collateral Value
Quantitative information about the significant unobservable inputs within Level 3
Loan held for investment, measurement input	26,500,000
Maximum | AFS Securities | Level 3 | Recurring | Indication from Market Maker | Price
Quantitative information about the significant unobservable inputs within Level 3
Debt securities, available-for-sale, measurement input	1	1