Dividends and Basic Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended		6 Months Ended
	Jul. 02, 2018	May 08, 2018	Jul. 01, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 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				$ 10,550	$ 8,187	$ 20,491	$ 16,008
Weighted Average Number of Common Shares Outstanding (in shares)				817,893	808,704	815,114	808,347
Basic Earnings Per Common Share Amount (in dollars per share)				$ 12.90	$ 10.12	$ 25.14	$ 19.80
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%
Dividends payable, date of record						Jun. 08, 2018
Mid-Year Cash Dividend Declared in 2018 [Member] | Subsequent Event [Member]
Dividends [Abstract]
Cash dividends paid per share of common stock (in dollars per share)	$ 6.90
Dividends payable, date paid	Jul. 02, 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