LOANS AND ALLOWANCE FOR CREDIT LOSSES - Non Traditional Mortgage Loans Additional Information (Details) $ in Thousands	12 Months Ended
Dec. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 5,898,405	$ 5,951,885
FICOR score decrease (percent)	10.00%
Loan Portfolio \| Loan Portfolio Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage to total loans and leases (percent)	100.00%	100.00%
NTM Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 437,113	$ 600,656
NTM Loans \| Loan Portfolio \| Loan Portfolio Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage to total loans and leases (percent)	7.40%	10.10%
NTM Loans \| Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 437,113	$ 600,656
Increase (decrease) in loans receivable	$ (163,500)
Increase (decrease) in loans receivable (percent)	(27.20%)
NTM Loans \| Consumer \| First lien
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 435,515	598,357
NTM Loans \| Consumer \| Green Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 33,200	52,300
Interest only notes balloon payment period	15 years
NTM Loans \| Consumer \| Green Loans \| First lien
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 31,587	49,959
NTM Loans \| Consumer \| Green Loans \| Nonperforming Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,000	1,500
NTM Loans \| Consumer \| Interest Only
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	401,600	545,400
NTM Loans \| Consumer \| Interest Only \| First lien
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	401,640	545,371
NTM Loans \| Consumer \| Interest Only \| Nonperforming Financing Receivables \| First lien
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,700	11,500
NTM Loans \| Consumer \| Negative amortization
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,300	3,000
NTM Loans \| Consumer \| Negative amortization \| First lien
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 2,288	$ 3,027
Number of non-performing loans \| loan	0	0

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