Senior Notes (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Senior Notes [Line Items]
Principal Amount, Net of Unamortized Deferred Financing Costs	$ 2,449,588		$ 2,448,439
Interest Costs Capitalized	$ 4,900	$ 4,500
6.125% Senior Notes due 2022 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage	6.125%
Principal Amount	$ 476,796		476,796
Unamortized Deferred Financing Costs	(3,671)		(3,921)
Principal Amount, Net of Unamortized Deferred Financing Costs	$ 473,125		472,875
5.0% Senior Notes due 2024 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage	5.00%
Principal Amount	$ 500,000		500,000
Unamortized Deferred Financing Costs	(4,457)		(4,688)
Principal Amount, Net of Unamortized Deferred Financing Costs	$ 495,543		495,312
5.625% Senior Notes due 2025 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage	5.625%
Principal Amount	$ 500,000		500,000
Unamortized Deferred Financing Costs	(5,582)		(5,808)
Principal Amount, Net of Unamortized Deferred Financing Costs	$ 494,418		494,192
6.75% Senior Notes due 2026 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage	6.75%
Principal Amount	$ 500,000		500,000
Unamortized Deferred Financing Costs	(6,198)		(6,407)
Principal Amount, Net of Unamortized Deferred Financing Costs	$ 493,802		493,593
6.625% Senior Notes due 2027 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage	6.625%
Principal Amount	$ 500,000		500,000
Unamortized Deferred Financing Costs	(7,300)		(7,533)
Principal Amount, Net of Unamortized Deferred Financing Costs	492,700		492,467
Senior Notes
Senior Notes [Line Items]
Principal Amount	2,476,796		2,476,796
Unamortized Deferred Financing Costs	(27,208)		(28,357)
Principal Amount, Net of Unamortized Deferred Financing Costs	$ 2,449,588		$ 2,448,439

Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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