Common Stock (details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Common Stock Shares Authorized	100,000,000	100,000,000
Reserved Shares Employee Stock Purchase Plan	137,798
Reserved Shares Dividend Reinvestment	197,112
Reserved Shares Stock Options	529,925	579,225	490,460	484,935
Date Through Which Entity May Repurchase Stock Under Board Authorization	May 2013
Aggregate Authorized Shares To Repurchase	2,800,000
Aggregate Authorized Value Of Shares To Repurchase	$ 100,000,000
Treasury Stock, Shares	2,100,000
Treasury Stock Program	$ 83,300,000
Common Stock Shares Issued Table [Abstract]
Common Stock, Shares, Outstanding	26,917,000	26,756,000	26,668,000	26,533,000
Stock Issued During Period, Shares, Employee Stock Purchase Plans	18,000	15,000	24,000
Common Stock Issued During Period Shares Stock Options Exercised	47,000	24,000	111,000
Stock Issued During Period, Shares, Dividend Reinvestment Plan	96,000	49,000