Summary of Accounting Policies - Additional Information (Detail)		12 Months Ended
	Nov. 30, 2017	Dec. 31, 2018 USD ($) Segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of operating segments | Segment		1
Number of reportable segments | Segment		1
Principal and interest default period		90 days
Period of principal and interest payments in arrears for open-end consumer loans are reviewed for charge-off		4 months
Residential mortgage loans are placed on non-accrual status at the time principal and interest period		90 days
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		19,900,000	$ 23,000,000
Originated mortgage servicing rights		68,000	88,000
Goodwill likelihood probability percentage	50.00%
Bank owned life insurance		110,052,000	107,489,000
Income on bank owned life insurance		3,256,000	2,354,000	$ 2,562,000
Company's liability to trusts including investments		$ 30,000,000
Cumulative adjustment for adoption					$ 0
Percentage of capital permitted for trust preferred securities		25.00%
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative adjustment for adoption			2,000,000		2,043,000
Accumulated Other Comprehensive Income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative adjustment for adoption			(420,000)		$ (2,043,000)
ASU 2018-02 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative adjustment for adoption			420,000
ASU 2018-02 | Accumulated Other Comprehensive Income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative adjustment for adoption			$ 420,000