LOANS AND LEASES AND ALLOWANCE FOR LOAN AND LEASE LOSSES - Non Traditional Mortgage Loans Additional Information (Details)	3 Months Ended
	Mar. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan	Mar. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 7,557,200,000	$ 7,700,873,000	$ 6,930,507,000
NTM Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	790,405,000	826,731,000
Consumer \| NTM Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 790,405,000	826,731,000
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 and leases	$ 720,100,000	$ 753,100,000
Number of non-performing loans \| loan	0	0
Nonperforming Financial Instruments \| Consumer \| NTM Loans \| Green Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 292,000	$ 0
Green Loans (HELOC) - first liens \| Consumer \| NTM Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	788,054,000	824,318,000
Green Loans (HELOC) - first liens \| Consumer \| NTM Loans \| Green Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	64,444,000	67,729,000
Green Loans (HELOC) - first liens \| Consumer \| NTM Loans \| Interest Only Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	720,116,000	753,061,000
Green Loans (HELOC) - first liens \| Consumer \| NTM Loans \| Negative amortization
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 3,494,000	$ 3,528,000
Number of non-performing loans \| loan	0	0