Loans and Allowance for Loan Losses - Additional Information (Detail)		12 Months Ended
	Apr. 22, 2019 USD ($)	Dec. 31, 2019 USD ($) Pool	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Accounts Notes And Loans Receivable [Line Items]
Loans		$ 2,544,420,000	$ 2,563,954,000
Loans purchased at discount		624,747,000	827,676,000	$ 796,064,000
Discount associated with loans purchased		8,287,000	11,372,000	7,231,000
Provision for loan losses	$ 14,500,000	18,354,000	3,961,000	2,953,000
Trouble debt restructurings, Impairment recognized		4,994,000
Interest income recognized		0
Outstanding commitments on loans		0
Consumer Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Over-draft deposit accounts		815,000	1,279,000
Purchased Credit Impaired Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Accretable yield		3,127,000	3,785,000	1,980,000
Interest income recognized		2,227,000	1,096,000	1,785,000
Provision for loan losses		628,000	714,000	$ 194,000
Residential Real Estate Loan Pools [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans		144,554,000	$ 64,558,000
Payments to acquire loans		$ 130,502,000
Purchased pools of residential real estate | Pool		8