Stock Repurchase Program (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	9 Months Ended			12 Months Ended	13 Months Ended	0 Months Ended		3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2011 2010 Stock Repurchase Program [Member]	Dec. 31, 2011 2010 Stock Repurchase Program [Member]	Apr. 30, 2011 2010 Stock Repurchase Program [Member]	Mar. 08, 2012 2011 Stock Repurchase Program [Member]	May 02, 2011 2011 Stock Repurchase Program [Member]	Sep. 30, 2012 2011 Stock Repurchase Program [Member]	Sep. 30, 2012 2011 Stock Repurchase Program [Member]	Dec. 31, 2011 2011 Stock Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount				$ 300,000,000		$ 323,700,000	$ 300,000,000
Treasury stock shares acquired			4,900		10,800			1,500	2,100
Treasury stock value acquired cost method	69,330,000	325,212,000	149,800,000		300,000,000			36,100,000	50,000,000
Average price of repurchased stock per share					$ 27.80
Stock repurchase program remaining authorized repurchase amount									$ 350,000,000	$ 76,300,000