Common Stock (details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
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	155,955
Reserved Shares Dividend Reinvestment	293,246
Reserved Shares Stock Options	1,159,875
Date Through Which Entity May Repurchase Stock Under Board Authorization	May 2012
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	26,756,000	26,668,000	26,533,000	26,501,000
Stock Issued During Period, Shares, Employee Stock Purchase Plans	15,000	24,000	9,000
Common Stock Issued During Period Shares Stock Options Exercised	24,000	111,000	23,000
Stock Issued During Period, Shares, Dividend Reinvestment Plan	49,000