Indebtedness (Convertible Senior Notes) (Details) (USD $)	3 Months Ended		3 Months Ended		3 Months Ended
	Jun. 30, 2011	Dec. 31, 2011	Jun. 30, 2012 2007 Notes [Member]	Dec. 31, 2011 2007 Notes [Member]	Jun. 30, 2012 2007 Notes [Member] Maximum [Member]	Jun. 30, 2012 Net-Share Settlement Terms Member [Member] 2007 Notes [Member] D
Convertible Senior Notes [Line Items]
Principal amount			$ 575,000,000	$ 575,000,000
Stated interest percentage on convertible senior notes			3.00%
Number of common shares per convertible notes			9,400,000		13,200,000
Debt instrument convertible into share at price per share			$ 61.07		$ 43.62
Convertible debt conversion rate per share					22.93
Observation period, days						20
Trading and business day period, days						5
Percent of trading price per note below reported sale price						97.00%
Minimum number of trading days						20
Number of consecutive trading days						30
Percent of applicable conversion price						130.00%
Percent of designated event repurchase price over principal amount of notes			100.00%
Notes, fair value			585,400,000	514,300,000
Convertible debt instrument amount allocated to equity		180,300,000	180,300,000
Debt issuance costs			$ 3,100,000	$ 3,900,000
Effective interest rate on net carrying value of 2007 Notes	9.30%		9.30%