Fair Value Measurements (Schedule of Fair Value of Debt Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
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	0
Four Point Three Seven Five Percent Convertible Senior Notes [Member]
Schedule of Fair Value of Debt Instruments [Line Items]
Convertible Debt	73,750	73,750
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	606,000
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	308,250	0
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 Convertible Senior Notes	73,842	73,013
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	595,151	594,535
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	0
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]
Convertible Debt	$ 72,657	$ 69,951