FAIR VALUE MEASURES - Summary of Significant Unobservable Inputs Used in Fair Value Measurement of Level 3 Assets and Liabilities (Details) $ in Thousands	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale, at fair value, net of allowance for credit losses of $112 and $0	$ 982,879	$ 1,403,403
Total impaired loans		104,733
Fair Value, Measurements, Recurring \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale, at fair value, net of allowance for credit losses of $112 and $0	1,170	1,500
Fair Value, Measurements, Nonrecurring \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total impaired loans	98,426	43,788
Other real estate owned	4,964	$ 17,289
Mortgage servicing rights	$ 130,630
Discounted par values \| Probability of default \| Fair Value, Measurements, Recurring \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale, measurement input	0.188	0
Discounted par values \| Probability of default \| Fair Value, Measurements, Recurring \| Weighted Average \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale, measurement input	0.188	0
Discounted par values \| Loss given default \| Fair Value, Measurements, Recurring \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale, measurement input	0.40
Discounted par values \| Loss given default \| Fair Value, Measurements, Recurring \| Weighted Average \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale, measurement input	0.40
Third-party appraisals and discounted cash flows \| Collateral discounts and discount rates \| Fair Value, Measurements, Nonrecurring \| Minimum \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Impaired loans, measurement input	0.20	0.01
Third-party appraisals and discounted cash flows \| Collateral discounts and discount rates \| Fair Value, Measurements, Nonrecurring \| Maximum \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Impaired loans, measurement input	0.90	0.95
Third-party appraisals and discounted cash flows \| Collateral discounts and discount rates \| Fair Value, Measurements, Nonrecurring \| Weighted Average \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Impaired loans, measurement input	0.44	0.27
Third party appraisals and sales contracts \| Collateral discounts and estimated costs to sell \| Fair Value, Measurements, Nonrecurring \| Minimum \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other real estate owned, measurement input	0.15	0.09
Third party appraisals and sales contracts \| Collateral discounts and estimated costs to sell \| Fair Value, Measurements, Nonrecurring \| Maximum \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other real estate owned, measurement input	0.59	0.89
Third party appraisals and sales contracts \| Collateral discounts and estimated costs to sell \| Fair Value, Measurements, Nonrecurring \| Weighted Average \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other real estate owned, measurement input	0.28	0.31
Discounted cash flows \| Discount rate \| Fair Value, Measurements, Nonrecurring \| Minimum \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights measurement input	0.09
Discounted cash flows \| Discount rate \| Fair Value, Measurements, Nonrecurring \| Maximum \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights measurement input	0.12
Discounted cash flows \| Discount rate \| Fair Value, Measurements, Nonrecurring \| Weighted Average \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights measurement input	0.10
Discounted cash flows \| Prepayment speed \| Fair Value, Measurements, Nonrecurring \| Minimum \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights measurement input	0.14
Discounted cash flows \| Prepayment speed \| Fair Value, Measurements, Nonrecurring \| Maximum \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights measurement input	0.37
Discounted cash flows \| Prepayment speed \| Fair Value, Measurements, Nonrecurring \| Weighted Average \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights measurement input	0.19

Impaired Loans, Measurement Input

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- Definition

Mortgage Servicing Rights

+ References

No definition available.

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- Definition

Mortgage Servicing Rights Measurement Input

+ References

No definition available.

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- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
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- Definition

Value of input used to measure investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

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-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 14A
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- Definition

Value of input used to measure real estate owned by financial institution by financial institution which is not directly related to its business.

+ References

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- Definition

Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement.

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