Fair Value Measurements Fair Value of Debt (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$ 1,778,641	$ 1,744,028
Carrying Value	1,652,602	1,652,740
Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	1,276,252	1,276,390
Convertible Senior Subordinated Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	56,350	56,350
Term Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	320,000	320,000
Fair Value, Inputs, Level 1 [Member] | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	1,331,397	1,321,443
Fair Value, Inputs, Level 1 [Member] | Convertible Senior Subordinated Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	127,244	102,585
Fair Value, Inputs, Level 2 [Member] | Term Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$ 320,000	$ 320,000