Stockholder's Equity (Details) (USD $)	3 Months Ended		0 Months Ended		3 Months Ended	12 Months Ended	0 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Sep. 14, 2011 2% Senior Convertible Notes Due 2017 [Member]	Mar. 26, 2007 2% Senior Convertible Notes Due 2017 [Member]	Mar. 31, 2012 Open Market Purchases And Pre-Established Trading Plan [Member]	Dec. 31, 2011 Open Market Purchases And Pre-Established Trading Plan [Member]	Mar. 09, 2011 Share Repurchase Program [Member]	Mar. 09, 2011 Share Repurchase Program [Member] 2% Senior Convertible Notes Due 2017 [Member]
Accelerated Share Repurchases [Line Items]
Issuance of preferred stock	5,000,000	5,000,000
Share repurchase program, authorized amount			$ 200,000,000				$ 150,000,000
Convertible notes maturity date								2017
Interest on senior convertible notes	2.00%			2.00%				2.00%
Total number of shares repurchased					1,600,000	9,200,000
Average price per share of common stock repurchased					$ 31.13	$ 18.52
Cost of reacquired shares	$ 49,996,000				$ 50,000,000	$ 169,700,000