Dividends and Basic Earnings Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Dividends and Basic Earnings Per Common Share [Abstract]
Cash dividends	$ 9,723	$ 9,418	$ 9,158
Cash dividends per share of common stock (in dollars per share)	$ 12.50	$ 12.10	$ 11.75
Percentage increase in cash dividend per share (in hundredths)	3.30%
Earnings per share for the period [Abstract]
Net Income	$ 24,061	$ 23,349	$ 22,209
Average Number of Common Shares Outstanding (in shares)	777,882	778,648	779,424
Basic Earnings Per Common Share (in dollars per share)	$ 30.93	$ 29.99	$ 28.49