LOAN PORTFOLIO-Corporation's Aging of Purchased Credit Impaired Loans (Parenthetical) (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 8,858,123	$ 8,850,476	$ 8,886,873
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	3,163,208	3,290,957	3,296,031
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	3,750,202	3,809,622
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	1,522,662	1,614,972	1,568,808
Financial Asset Acquired with Credit Deterioration [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	146,640	158,174	165,818
Financial Asset Acquired with Credit Deterioration [Member] | Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	143,176	153,991	162,676
Financial Asset Acquired with Credit Deterioration [Member] | Commercial Portfolio Segment [Member] | Mortgage Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	3,464	4,183	$ 3,142
Financial Asset Acquired with Credit Deterioration [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	11,600	28,100
Financial Asset Acquired with Credit Deterioration [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Mortgage Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 0	$ 200