LOANS AND ALLOWANCE FOR LOAN LOSSES - Non Traditional Mortgage Loans Additional Information (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan	Sep. 30, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 6,383,259	$ 7,700,873	$ 7,253,293
NTM Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6,383,259	7,700,873
Consumer \| NTM Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 653,475	826,731
Consumer \| NTM Loans \| Green Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest only notes balloon payment period	15 years
Consumer \| NTM Loans \| Interest Only Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 588,600	753,100
Non-performing loans \| Consumer \| NTM Loans \| Green Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	286	0
Green Loans (HELOC) - first liens \| Consumer \| NTM Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	651,167	824,318
Green Loans (HELOC) - first liens \| Consumer \| NTM Loans \| Green Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	59,538	67,729
Green Loans (HELOC) - first liens \| Consumer \| NTM Loans \| Interest Only Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	588,567	753,061
Green Loans (HELOC) - first liens \| Consumer \| NTM Loans \| Negative amortization
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 3,062	$ 3,528
Number of nonperforming loans with negative amortization \| loan	0	0
Green Loans (HELOC) - first liens \| Non-performing loans \| Consumer \| NTM Loans \| Interest Only Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 827	$ 0