Earnings Per Share - Weighted Average Number of Shares Used in Computing Earnings Per Share (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Shares [Abstract]
Basic earnings per share (in shares)	3,793,366	3,783,322	3,772,421
Effect of dilutive stock awards (in shares)	5,450	7,396	6,945
Diluted earnings per share (in shares)	3,798,816	3,790,718	3,779,366
Per Share Amount [Abstract]
Basic earnings per share (in dollars per share)	$ 1.55	$ 1.80	$ 1.63
Diluted earnings per share (in dollars per share)	$ 1.55	$ 1.80	$ 1.62