Regulatory Matters - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Periodic increase of capital conservation buffer	0.625%
Total risk-based capital ratio, Actual Ratio	20.61%	19.85%
Tier1 Capital (to Risk-Weighted Assets), Actual Ratio	19.47%	18.66%
Common Tier1 Capital (to Risk-Weighted Assets), Actual Ratio	19.47%	18.66%
Tier1 Leverage ratio, Actual Ratio	11.85%	11.09%
Required tangible net assets	$ 2,000,000
Tangible net assets, total	22,503,000
Subsidiary bank's reserve balance	$ 11,372,000	$ 11,504,000
Minimum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer	0.625%
Maximum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer	2.50%