Stockholders' Equity Note (Details) (USD $)	1 Months Ended			12 Months Ended
	Apr. 30, 2012	Aug. 31, 2011	Apr. 30, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stockholders' Equity Note [Abstract]
Number of votes per share of common stock				1
Number of shares of common stock available for issuance				6,400,000
Amount of common stock repurchases authorized	$ 400,000,000		$ 150,000,000
Increase in stock repurchase authorized amount	150,000,000	250,000,000
Value of shares repurchased during period				141,468,000	324,733,000	91,960,000
Remaining amount available for future purchases of shares under approved repurchase program.					$ 38,500,000
Common Stock [Member]
Statement [Line Items]
Repurchases of common stock, shares				4,360,103	12,276,878	2,452,595