Securities - Schedule of Allowance for Credit Losses on Held-to-maturity Securities (Detail)	12 Months Ended
	Dec. 31, 2020 USD ($)
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items]
Ending balance at December 31, 2020	$ 326,000
Residential Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Sponsored Entities and Agencies [Member]
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items]
Ending balance at December 31, 2020	0
ASU 2016-13 [Member]
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items]
Beginning balance at January 1, 2020	229,000
Current period provision	97,000
Ending balance at December 31, 2020	326,000
ASU 2016-13 [Member] | Obligations of State and Political Subdivisions [Member]
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items]
Beginning balance at January 1, 2020	96,000
Current period provision	34,000
Ending balance at December 31, 2020	130,000
ASU 2016-13 [Member] | Corporate Debt Securities [Member]
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items]
Beginning balance at January 1, 2020	133,000
Current period provision	63,000
Ending balance at December 31, 2020	$ 196,000