Long-term Debt - Summary of Long-term Debt (Details) - Senior Notes [Member] - USD ($)	Mar. 31, 2016	Dec. 31, 2015
5.50% Senior Notes [Member]
Debt Instrument [Line Items]
Principal Amount at Par	$ 700,000,000
Fair Value	$ 732,900,000	$ 717,500,000
Interest rate	5.50%
5.875% Senior Notes [Member]
Debt Instrument [Line Items]
Principal Amount at Par	$ 800,000,000
Fair Value	$ 842,000,000	820,000,000
Interest rate	5.875%
5.750% Senior Notes [Member]
Debt Instrument [Line Items]
Principal Amount at Par	$ 400,000,000
Fair Value	$ 422,000,000	411,000,000
Interest rate	5.75%
5.375% Senior Notes [Member]
Debt Instrument [Line Items]
Principal Amount at Par	$ 500,000,000
Fair Value	$ 521,900,000	$ 525,000,000
Interest rate	5.375%