Dividends and Basic and Diluted Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		9 Months Ended
	May 13, 2021	Jul. 01, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Dividends [Abstract]
Cash dividends declared per share of common stock (in dollars per share)					$ 7.50	$ 7.25
Basic Earnings per Common Share [Abstract]
Net Income			$ 17,502	$ 14,810	$ 50,368	$ 43,241
Weighted Average Number of Common Shares Outstanding (in shares)			789,646	793,556	789,646	793,539
Basic Earnings Per Common Share (in dollars per share)			$ 22.16	$ 18.66	$ 63.79	$ 54.49
Diluted Earnings Per Common Share (in dollars per share)			$ 22.16	$ 18.66	$ 63.79	$ 54.49
Mid-Year Cash Dividend Declared in 2021 [Member]
Dividends [Abstract]
Dividend, declared date					May 13, 2021
Cash dividends declared per share of common stock (in dollars per share)	$ 7.50
Percentage increase in cash dividend per share	3.40%
Dividends payable, date paid					Jul. 01, 2021
Dividend, record date					Jun. 11, 2021
Mid-Year Cash Dividend Declared in 2020 [Member]
Dividends [Abstract]
Cash dividends paid per share of common stock (in dollars per share)		$ 7.25
Dividends payable, date paid					Jul. 01, 2020