Commitments and Contingencies - Additional Information (Detail)	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) transaction	Dec. 31, 2019 USD ($) transaction	Dec. 31, 2018 USD ($)
Other Commitments [Line Items]
Commitments of lending operations									$ 0	$ 0
Commitments to sell residential mortgages	$ 91,900,000				$ 60,000,000.0				91,900,000	60,000,000.0
Provision for credit losses	$ (936,000)	$ 2,716,000	$ 94,754,000	$ 56,646,000	$ 1,590,000	$ 4,121,000	$ 12,195,000	$ 7,654,000	153,180,000	$ 25,560,000	$ 13,170,000
Loans repurchased during period									200,000
Secondary Market Loan Sales
Other Commitments [Line Items]
Provision for credit losses									$ 0
Number of loans repurchased | transaction									0	1
Minimum
Other Commitments [Line Items]
Closing period of residential mortgage commitments									1 month
Maximum
Other Commitments [Line Items]
Closing period of residential mortgage commitments									6 months
Real Estate
Other Commitments [Line Items]
Commitments of lending operations									$ 521,100,000
Commitments to Extend Credit
Other Commitments [Line Items]
Commitments of lending operations									2,400,000,000
Consumer(3)
Other Commitments [Line Items]
Commitments of lending operations									$ 591,900,000