Accounting for Certain Loans Acquired in a Transfer - Additional Information (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Total provision charged to operating expense	$ 340,000	$ 376,000	$ 896,000	$ 364,000	$ 528,000	$ 1,176,000	$ 635,000	$ 567,000	$ 1,976,000	$ 2,906,000	$ 2,470,000
Loans Purchased With Evidence of Credit Deterioration [Member]
Business Acquisition [Line Items]
Total provision charged to operating expense									133,000	60,000
Allowances for loan losses									$ 0	$ 0