Fair Value Measurements (Schedule of Fair Value of Debt Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Eight Point Six Two Five Percent Senior Notes [Member]
Schedule of Fair Value of Debt Instruments [Line Items]
Senior Notes	$ 600,000	$ 600,000
Seven Point Five Percent Senior Notes [Member]
Schedule of Fair Value of Debt Instruments [Line Items]
Senior Notes	300,000	300,000
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Eight Point Six Two Five Percent Senior Notes [Member]
Schedule of Fair Value of Debt Instruments [Line Items]
Senior Notes	596,000	595,822
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Seven Point Five Percent Senior Notes [Member]
Schedule of Fair Value of Debt Instruments [Line Items]
Senior Notes	300,000	300,000
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Four Point Three Seven Five Percent Convertible Senior Notes [Member]
Schedule of Fair Value of Debt Instruments [Line Items]
Other long-term debt	4,425	4,425
Portion at Fair Value, Fair Value Disclosure [Member] | Eight Point Six Two Five Percent Senior Notes [Member]
Schedule of Fair Value of Debt Instruments [Line Items]
Fair value of Senior Notes	645,000	644,978
Portion at Fair Value, Fair Value Disclosure [Member] | Seven Point Five Percent Senior Notes [Member]
Schedule of Fair Value of Debt Instruments [Line Items]
Fair value of Senior Notes	330,000	327,000
Portion at Fair Value, Fair Value Disclosure [Member] | Four Point Three Seven Five Percent Convertible Senior Notes [Member]
Schedule of Fair Value of Debt Instruments [Line Items]
Fair Value of Other long-term debt	$ 4,182	$ 4,115