Treasury Stock (Details) (USD $)	1 Months Ended		6 Months Ended			3 Months Ended	9 Months Ended
	Aug. 31, 2012	May 31, 2008	Jul. 01, 2012	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 August 2012 Program [Member]	Sep. 30, 2012 May 2008 Program [Member]
Treasury Stock (Additional Textual) [Abstract]
Shares repurchased						91,186	574,153
Treasury Stock (Textual) [Abstract]
Shares repurchased, Per Share	$ 13	$ 13
Cost of common stock held in treasury (2012 - 21,389,445 and 2011 -20,724,106 shares)				$ (307,134,000)	$ (300,584,000)
Common stock held in treasury, shares				21,389,445	20,724,106
Approximate shares available for future issuances				7,600,000
Shares repurchased under Board of Directors authorized program	1,000,000	1,000,000
Authorization Expiration	The authorization has no expiration	The authorization has no expiration
Shares repurchased under Board of Directors authorized program, value			$ 5,000,000