Summary of Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019 USD ($) Segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Accounting Policies [Abstract]
Number of operating segments | Segment	1
Number of reportable segments | Segment	1
Principal and interest default period	90 days
Residential mortgage loans are placed on non-accrual status at the time principal and interest period	90 days
Period of principal and interest payments in arrears for open-end consumer loans are reviewed for charge-off	4 months
Non-accrual asset satisfactory payments period	6 months
Non-accrual loans with recorded investment, minimum amount	$ 500,000
Maximum amount of individual impaired commercial loans that places into homogeneous pool for collective evaluation	500,000
Amount of loans sold that are being serviced for others	18,600,000	$ 19,900,000
Originated mortgage servicing rights	43,000	68,000
Goodwill	156,277,000	136,433,000
Bank owned life insurance	112,392,000	110,052,000
Income on bank owned life insurance	2,740,000	$ 3,256,000	$ 2,354,000
Company's liability to trusts including investments	$ 30,000,000.0
Percentage of capital permitted for trust preferred securities	25.00%