Earnings Per Share - Reconciliation of Weighted Average Shares used for Basic and Diluted Earnings Per Share Calculation (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Basic weighted average common shares	19,288,996	19,248,657	19,208,978
Add: Other common shares eligible for common dividends:
Restricted stock and stock options	74,813	80,581	84,104
Diluted weighted average common shares	19,363,809	19,329,238	19,293,082