Earnings Per Share - Weighted Average Number of Shares Used in Computing Earnings Per Share (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Shares [Abstract]
Basic earnings per share (in shares)	3,783,322	3,772,421	3,764,690
Effect of dilutive stock awards (in shares)	7,396	6,945	8,320
Diluted earnings per share (in shares)	3,790,718	3,779,366	3,773,010
Per Share Amount [Abstract]
Basic earnings per share (in dollars per share)	$ 1.80	$ 1.63	$ 0.66
Diluted earnings per share (in dollars per share)	$ 1.80	$ 1.62	$ 0.66