LOANS AND LEASES AND ALLOWANCE FOR LOAN AND LEASE LOSSES - Non Traditional Mortgage Loans Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 6,226,897,000	$ 6,034,752,000	$ 6,568,791,000
Percentage decrease in credit score to run exception report	10.00%
Non-Traditional Mortgages (NTM)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 793,946,000	885,148,000
Consumer | Non-Traditional Mortgages (NTM)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	793,946,000	885,148,000
Increase (decrease) in loans receivable	$ (91,200,000)
Increase (decrease) in loans receivable, percentage	(10.30%)
Consumer | Non-Traditional Mortgages (NTM) | Green Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 85,800,000	91,000,000
Interest only notes balloon payment period	15 years
Consumer | Non-Traditional Mortgages (NTM) | Green Loans | Nonperforming Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 0	0
Consumer | Non-Traditional Mortgages (NTM) | Interest Only Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	704,400,000	784,400,000
Consumer | Non-Traditional Mortgages (NTM) | Interest Only Loans | Nonperforming Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,200,000	467,000
Consumer | Non-Traditional Mortgages (NTM) | Negative amortization
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,700,000	9,800,000
Consumer | Non-Traditional Mortgages (NTM) | Negative amortization | Nonperforming Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 0	$ 0
Consumer | Non-Traditional Mortgages (NTM) | Loan Portfolio | Loan Portfolio Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	12.80%	14.70%