LOAN PORTFOLIO - Corporation's Commercial Credit Exposure (Parenthetical) (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable Recorded Investment [Line Items]
Loans held for sale	$ 33,175	$ 43,186
Commercial Portfolio Segment [Member] | Commercial And Industrial Sector [Member]
Financing Receivable Recorded Investment [Line Items]
Loans held for sale	0	1,725
Commercial Portfolio Segment [Member] | Construction Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans held for sale	0
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member]
Financing Receivable Recorded Investment [Line Items]
Loans held for sale	7,381	11,371
Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans held for sale	7,400	16,100
Nonaccrual [Member] | Commercial Portfolio Segment [Member] | Commercial And Industrial Sector [Member]
Financing Receivable Recorded Investment [Line Items]
Loans held for sale		1,700
Nonaccrual [Member] | Commercial Portfolio Segment [Member] | Construction Loans [Member] | Commercial Loan [Member]
Financing Receivable Recorded Investment [Line Items]
Loans held for sale		3,000
Nonaccrual [Member] | Commercial Portfolio Segment [Member] | Mortgage Receivable [Member]
Financing Receivable Recorded Investment [Line Items]
Loans held for sale	$ 7,400	$ 11,400