Loan Servicing - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Transfers And Servicing [Abstract]
Unpaid principal balances of residential mortgage loans serviced for others	$ 1,940,000,000		$ 1,760,000,000
Custodial Escrow balances	17,000,000.0		$ 14,200,000
Increase (reduced) the valuation allowance of mortgage servicing rights	$ (421,000)	$ 1,562,000