ALLOWANCE FOR LOAN AND LEASE LOSSES AND CREDIT QUALITY INFORMATION - Schedule of Residential and Consumer Credit Exposure (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans		$ 8,464,562
Total		100.00%
Accrued troubled debt restructured loans		$ 14,000
Reverse mortgage, fair value	$ 16,100	16,600	$ 15,900
Acquired nonimpaired loans		3,200,000	$ 3,699,730
Total Residential and Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans		$ 2,128,610
Total		100.00%
Acquired nonimpaired loans		$ 1,100,000
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans		999,879
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans		1,128,731
Nonperforming | Total Residential and Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans		$ 20,232
Total		1.00%
Nonperforming | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans		$ 12,858
Nonperforming | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans		7,374
Performing | Total Residential and Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans		$ 2,098,925
Total		99.00%
Performing | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans		$ 979,695
Performing | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans		$ 1,119,230
Risk Rating
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0.00%
Risk Rating | Total Residential and Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans		$ 9,453
Total		0.00%
Risk Rating | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans		$ 7,326
Risk Rating | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans		$ 2,127