Fair Value of Financial Instruments (Details 2) (USD $)			1 Months Ended	3 Months Ended
Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2010 Convertible Senior Subordinated Notes 3.35 Percent Due 2015	Mar. 31, 2012 Convertible Senior Subordinated Notes 3.35 Percent Due 2015
Debt Offerings, Fair Value Disclosure
Convertible senior subordinated notes (due 2015)	$ 400,000,000	$ 400,000,000	$ 400,000,000	$ 400,000,000
Interest rate (as a percent)			3.35%	3.35%
Fair value of convertible senior subordinated notes				$ 458,000,000

Stated interest rate of the subordinated debt.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Chapter 4

-Paragraph 80

-Subparagraph Exhibit 4-8, 9

-IssueDate 2006-05-01

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Chapter 4

-Paragraph 08

-IssueDate 2006-05-01

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration