Commitments and Contingencies - Additional Information (Detail)	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($) institution loan	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) loan	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) transaction institution loan	Dec. 31, 2018 USD ($) transaction loan	Dec. 31, 2017 USD ($)
Other Commitments [Line Items]
Commitments of lending operations									$ 0	$ 0
Commitments to sell residential mortgages	$ 60,000,000.0				$ 32,400,000				60,000,000.0	32,400,000
Provision for loan and lease losses	$ 1,590,000	$ 4,121,000	$ 12,195,000	$ 7,654,000	$ 3,306,000	$ 3,716,000	$ 2,498,000	$ 3,650,000	$ 25,560,000	$ 13,170,000	$ 10,964,000
Number of unrelated financial institutions | institution	5								5
Derivative transaction held for guarantee | loan	172				136				172	136
Notional	$ 502,172,000				$ 167,933,000				$ 502,172,000	$ 167,933,000
Aggregate fair value of swaps to customers	26,400,000				300,000				26,400,000	$ 300,000
Number of customers in paying position to third party | transaction										50
Amount of swap liability in paying positions to third party					4,600,000					$ 4,600,000
Reserves for swap guarantees	$ 0				0				$ 0	0
Interest Rate Swap
Other Commitments [Line Items]
Derivative transaction held for guarantee | loan	156								156
Notional	$ 941,000,000.0				$ 581,500,000				$ 941,000,000.0	$ 581,500,000
Aggregate fair value of swaps to customers	$ 27,400,000								27,400,000
Secondary Market Loan Sales
Other Commitments [Line Items]
Provision for loan and lease losses									$ 0
Number of loans repurchased | transaction									1	0
Loans repurchased during period									$ 200,000
Minimum
Other Commitments [Line Items]
Closing period of residential mortgage commitments									1 month
Notional amount maturity period									1 year	1 year
Maximum
Other Commitments [Line Items]
Closing period of residential mortgage commitments									6 months
Notional amount maturity period									15 years	11 years
Real Estate
Other Commitments [Line Items]
Commitments of lending operations									$ 484,400,000
Commitments to Extend Credit
Other Commitments [Line Items]
Commitments of lending operations									2,100,000,000
Consumer
Other Commitments [Line Items]
Commitments of lending operations									$ 506,500,000