Dividends and Basic Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended		9 Months Ended
	Jul. 02, 2018	May 08, 2018	Jul. 01, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Dividends [Abstract]
Cash dividends declared per share of common stock (in dollars per share)						$ 6.90	$ 6.75
Earnings per share for the period [Abstract]
Net Income				$ 12,000	$ 8,581	$ 32,491	$ 24,589
Weighted Average Number of Common Shares Outstanding (in shares)				793,418	810,291	807,129	809,002
Basic Earnings Per Common Share Amount (in dollars per share)				$ 15.12	$ 10.59	$ 40.26	$ 30.39
Mid-Year Cash Dividend Declared in 2018 [Member]
Dividends [Abstract]
Dividends payable, date declared						May 08, 2018
Cash dividends declared per share of common stock (in dollars per share)		$ 6.90
Percentage increase in cash dividend per share		2.20%
Cash dividends paid per share of common stock (in dollars per share)	$ 6.90
Dividends payable, date paid						Jul. 02, 2018
Dividends payable, date of record						Jun. 08, 2018
Mid-Year Cash Dividend Declared in 2017 [Member]
Dividends [Abstract]
Cash dividends paid per share of common stock (in dollars per share)			$ 6.75
Dividends payable, date paid						Jul. 01, 2017