Dividends and Basic Earnings Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Dividends and Basic Earnings Per Common Share [Abstract]
Dividends Payable, Date Declared			May 17, 2013
Cash dividends per share of common stock (in dollars per share)			$ 6.20	$ 5.90
Percentage increase in cash dividend per share (in hundredths)			5.10%
Dividends payable, date paid			Jul. 01, 2013	Jul. 02, 2012
Dividends Payable, Date of Record			Jun. 10, 2013
Earnings per share for the period [Abstract]
Net Income	$ 6,352	$ 6,332	$ 18,168	$ 17,684
Average Number of Common Shares Outstanding (in shares)	777,882	778,487	777,882	779,906
Basic Earnings Per Common Share (in dollars per share)	$ 8.17	$ 8.13	$ 23.36	$ 22.70