Senior Notes (Schedule of Senior Notes) (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Carrying Value	$ 1,628,300,000	$ 850,800,000
Senior Notes [Member]
Debt Instrument [Line Items]
Face Value	705,000,000	405,000,000
Unamortized Premium/(Discount)	1,100,000	4,000,000
Carrying Value	706,100,000	409,000,000
Senior Notes [Member] | 7.75% Senior Notes Due 2042 [Member]
Debt Instrument [Line Items]
Interest Rate	7.75%
Face Value	55,000,000	55,000,000
Unamortized Premium/(Discount)	0	0
Carrying Value	55,000,000	55,000,000
Senior Notes [Member] | 5.875% Senior Notes Dues April 2024 [Member]
Debt Instrument [Line Items]
Interest Rate	5.875%
Face Value	300,000,000	0
Unamortized Premium/(Discount)	(2,800,000)	0
Carrying Value	297,200,000
Senior Notes [Member] | 8.75% Senior Notes, Due 2019 [Member]
Debt Instrument [Line Items]
Interest Rate	8.75%
Face Value	350,000,000	350,000,000
Unamortized Premium/(Discount)	3,900,000	4,000,000
Carrying Value	$ 353,900,000	$ 354,000,000