Senior Notes - Schedule of Senior Notes (Details) - Senior Notes [Member] - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Face Value	$ 705,000,000	$ 705,000,000
Unamortized Net Premium/(Discount)	(2,500,000)	(2,600,000)
Carrying Value	$ 702,500,000	702,400,000
7.75% Senior Notes Due 2042 [Member]
Debt Instrument [Line Items]
Interest Rate	7.75%
Face Value	$ 55,000,000	55,000,000
Unamortized Net Premium/(Discount)	0	0
Carrying Value	$ 55,000,000	55,000,000
5.875% Senior Notes Dues April 2024 [Member]
Debt Instrument [Line Items]
Interest Rate	5.875%
Face Value	$ 650,000,000	650,000,000
Unamortized Net Premium/(Discount)	(2,500,000)	(2,600,000)
Carrying Value	$ 647,500,000	$ 647,400,000