FAIR VALUE MEASURES - Fair Value Measurements of Assets Measured at Fair Value on Non-Recurring Basis (Details) - Fair Value, Measurements, Nonrecurring - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	$ 272,780	$ 61,077
Collateral-dependent loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	148,083	43,788
Other real estate owned
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	4,239	17,289
Mortgage servicing rights
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	114,396
SBA servicing rights
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	6,062
Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	0	0
Level 1 | Collateral-dependent loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	0	0
Level 1 | Other real estate owned
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	0	0
Level 1 | Mortgage servicing rights
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	0
Level 1 | SBA servicing rights
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	0
Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	120,458	0
Level 2 | Collateral-dependent loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	0	0
Level 2 | Other real estate owned
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	0	0
Level 2 | Mortgage servicing rights
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	114,396
Level 2 | SBA servicing rights
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	6,062
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	152,322	61,077
Level 3 | Collateral-dependent loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	148,083	43,788
Level 3 | Other real estate owned
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	4,239	$ 17,289
Level 3 | Mortgage servicing rights
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	0
Level 3 | SBA servicing rights
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value	$ 0