Dividends and Earnings Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Dividends and Basic Earnings Per Common Share [Abstract]
Cash dividends (in dollars per share)			$ 5.90	$ 5.65
Percentage increase in cash dividend from prior period (in hundredths)			4.40%
Basic earnings per common share [Abstract]
Net Income	$ 6,332	$ 6,267	$ 17,684	$ 16,548
Average Number of Common Shares Outstanding (in shares)	778,487	779,424	779,906	779,424
Basic Earnings Per Common Share Amount (in dollars per share)	$ 8.13	$ 8.04	$ 22.70	$ 21.23