Convertible Debt (Details) (USD $)	12 Months Ended			1 Months Ended		1 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Oct. 31, 2011 Call Option [Member]	Oct. 31, 2011 Warrant Transactions [Member]	Oct. 17, 2011 Convertible Senior Notes [Member] Integer Decimal Percent	Dec. 31, 2011 Convertible Senior Notes [Member]	Oct. 31, 2011 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Principal amount								$ 400,000,000
Interest rate, stated percentage (in hundredths)						1.875%
Net proceeds from offering, net of discount and issuance costs	391,107,000	0	0
Initial conversion rate						11.9021
Increment of principal amount of conversion						1,000
Total shares upon conversion (in shares)						4,760,840
Initial conversion price (in dollars per share)						$ 84.02
Terms of conversion feature						A holder of the Notes may surrender their Notes at their option any time prior to the close of business on the business day immediately preceding July 1, 2016, only under the following circumstances: (i) during any calendar quarter commencing after the calendar quarter ending on December 31, 2011 (and only during such calendar quarter), if the last reported sale price of the Company's Common Stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day; (ii) during the five business day period after any ten consecutive trading day period (the "measurement period") in which the trading price, as defined, of the Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of the Company's Common Stock and the conversion rate on each such trading day; (iii) if the Company elects to issue to all or substantially all holders of its Common Stock any right, options or warrants (other than pursuant to a rights plan) entitling them for a period of not more than 60 calendar days after the record date for such issuance, to subscribe for or purchase shares of the Company's Common Stock, at a price per share less than the average of the last reported sales prices of the Company's Common Stock for the ten consecutive day period ending on, and including, the trading day immediately preceding the declaration date for such issuance; (iv) upon specified distributions to the Company's shareholders; or (v) upon the occurrence of specified corporate transactions, such as a fundamental change (i.e., a change in control), or the Company's Common Stock ceasing to be listed on at least one U.S. national securities exchange. On or after July 1, 2016, holders may convert their Notes at the conversion rate at any time prior to the close of business on the second scheduled trading day immediately preceding the maturity date irrespective of the foregoing conditions.
Percentage of principal value that holders can require the Company to repurchase (in hundredths)						100.00%
Estimated fair value of the Liability Component						271,100,000
Carrying amount of Equity Component						120,900,000
Effective interest rate used to amortize the discount on the liability component (in hundredths)						10.20%
Net carrying amount of the liability component [Abstract]
Total convertible senior notes - par							400,000,000
Unamortized discount							124,981,000
Net carrying amount of the liability component							275,019,000
Total interest expense [Abstract]
Contractual coupon interest rate							1,455,000
Amortization of discount and note issuance costs							3,944,000
Total interest expense							5,399,000
Fair value of the outstanding Notes	375,500,000
Gross proceeds from the issuance of the Notes						392,000,000
Issuance costs						900,000
Class of Warrant or Right [Line Items]
Strike price of the warrant transaction (in dollars per share)					$ 103.41
Proceeds received from the Warrant	93,800,000	0	0
Option Indexed to Issuer's Equity [Line Items]
Purchase of convertible note hedges				$ 117,500,000