Stockholders' Equity (Details 6) (USD $)	12 Months Ended				0 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jun. 30, 2008	Mar. 04, 2013 2013 Share Repurchase Program	Feb. 28, 2013 2013 Share Repurchase Program	Dec. 31, 2013 2013 Share Repurchase Program	Nov. 30, 2012 2012 Share Repurchase Program	Jul. 31, 2012 2012 Share Repurchase Program	Jun. 30, 2012 2012 Share Repurchase Program	May 31, 2012 Repurchase Program	Oct. 31, 2011 Repurchase Program
Share Repurchase
Authorized aggregate repurchases of common stock						$ 420,000,000				$ 100,000,000		$ 300,000,000
Period over which shares may be purchased under share repurchase program					1 year				1 year			2 years
Repurchased shares of common stock							708,998	2,000,000			2,000,000	4,700,000
Cost of shares repurchased	42,439,000	188,000,000					42,400,000
Cost of shares repurchased			$ 211,766,000								$ 88,000,000	$ 212,000,000
Shareholder Rights Plan
Purchase price of each Right, before the amendment and restatement of the Rights (in dollars per one one-thousandth of a share)				64.75
Purchase price of each Right, after the amendment and restatement of the Rights (in dollars per one one-thousandth of a share)				400.00
Number of shares of Series A Junior Participating Preferred Stock each Right entitles a holder to purchase				0.001
Minimum ownership percentage in the outstanding shares of voting stock from the commencement of a tender offer that would result in the exercise of shares under one condition of the Agreement (as a percent)				15.00%