Loans - Investment in Residential and Consumer Loans, Excluding Loans from Purchased Credit Impaired Loans (Detail) $ in Thousands	Dec. 31, 2019 USD ($)
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 2,512,544
Residential Real Estate [Member] | Performing TDRs [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	2,499,089
Residential Real Estate [Member] | Non-performing TDRs [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	13,455
Consumer and Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	247,307
Consumer and Other [Member] | Performing TDRs [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	246,387
Consumer and Other [Member] | Non-performing TDRs [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 920