Convertible Debt (Details) (USD $)	1 Months Ended	12 Months Ended
	Oct. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Convertible Debt [Abstract]
Proceeds received from the Warrant	$ 93,800,000		$ 93,800,000
Warrant transactions
Convertible Debt [Abstract]
Strike price of the warrant transaction (in dollars per share)	103.41
Proceeds received from the Warrant	93,800,000
Call option
Convertible Debt [Abstract]
Purchase of convertible note hedges	117,500,000
Debt Instrument, Redemption, Criteria One [Member]
Debt Instrument [Line Items]
Number of trading days		20 days
Number of consecutive trading days		30 days
Percentage of stock price trigger		130.00%
Debt Instrument, Redemption, Criteria Two [Member]
Debt Instrument [Line Items]
Number of trading days		5 days
Number of consecutive trading days		10 days
Percentage of stock price trigger		98.00%
Debt Instrument, Redemption, Criteria Three [Member]
Debt Instrument [Line Items]
Calendar day period after the record date of equity instruments issuance		60 days
Number of consecutive days		10 days
Convertible senior notes
Debt Instrument [Line Items]
Interest rate, stated percentage	1.875%	1.875%
Net proceeds from offering, net of discount and issuance costs	391,100,000
Initial conversion ratio	11.9021
Increment of principal amount for conversion	1,000
Total shares upon conversion (in shares)	4,760,840
Initial conversion price (in dollars per share)	$ 84.02
Percentage of principal value that holders can require Company to repurchase	100.00%
If-converted value in excess of principal		414,400,000
Estimated fair value of the liability component	271,100,000
Carrying amount of equity component	120,900,000
Gross proceeds from the issuance of the Notes	392,000,000
Effective interest rate used to amortize the discount on teh liability component	10.20%
Issuance costs	900,000
Net carrying amount of the liability component [Abstract]
Total convertible senior notes - par	400,000,000	400,000,000	400,000,000
Unamortized discount		(103,482,000)	(124,981,000)
Net carrying amount of the liability component		296,518,000	275,019,000
Interest Expense, Debt [Abstract]
Contractual coupon interest rate		7,503,000	1,455,000
Amortization of discount and note issuance costs		21,623,000	3,944,000
Total interest expense		$ 29,126,000	$ 5,399,000