Stockholder's Equity (Details) (USD $)	0 Months Ended	3 Months Ended		12 Months Ended			0 Months Ended
	Mar. 14, 2011	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2011	Dec. 31, 2010	Mar. 26, 2007 2% Senior Convertible Notes Due March 2017 [Member]	Sep. 14, 2011 Share Repurchase Program [Member]	Mar. 09, 2011 Share Repurchase Program [Member]	Sep. 14, 2011 Share Repurchase Program [Member] 2% Senior Convertible Notes Due March 2017 [Member]	Mar. 09, 2011 Share Repurchase Program [Member] 2% Senior Convertible Notes Due March 2017 [Member]
Accelerated Share Repurchases [Line Items]
Issuance of preferred stock, shares		5,000,000		5,000,000	5,000,000
Share repurchase program, authorized amount							$ 200,000,000	$ 150,000,000
Convertible notes maturity date									2017	2017
Interest on senior convertible notes						2.00%			2.00%	2.00%
Repurchase of common stock on accelerated basis	50,000,000
Total number of shares repurchased	2,700,000	1,000,000
Average price per share of common stock repurchased	$ 18.74	$ 20.62	$ 18.04
Treasury Stock, Shares, Acquired			5,500,000
Repurchase of shares, acquired	2,700,000	1,000,000
Payments for Repurchase of Common Stock	$ 50,000,000	$ 20,800,000	$ 98,900,000	$ 169,661,000