Subsequent Event (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2011
Subsequent Event [Line Items]
Subsequent event date	Oct. 17, 2011
Estimated net proceeds from offering	$ 391.3
Estimated net proceeds from offering, if the initial purchaser exercises its full option to purchase additional notes	450.1
Estimated cost of the initial convertible note hedge, net of proceeds from sale of warrant transaction	23.7
1.875% Convertible Senior Notes [Member]
Subsequent Event [Line Items]
Debt issued at par value	400
Stated interest rate (in hundredths)	1.875%
Maturity date	Oct. 01, 2016
Option period granted to initial purchaser, to purchase up to an additional aggregate principal amount of notes (in days)	13 D
Maximum amount available for purchase of additional aggregate principal amount of notes	$ 60
Frequency of periodic payment	The Notes will pay interest semi-annually on April 1 and October 1 at an annual rate of 1.875%
Initial conversion features for the notes	The initial conversion rate for the notes will be 11.9021 shares of Common Stock (subject to adjustment in certain circumstances) per $1,000 principal amount of the notes
Conversion price (in dollars per share)	$ 84.02
Warrant [Member]
Subsequent Event [Line Items]
Strike price of the warrant transaction (in dollars per share)	$ 103.41