Long-term Debt Senior Notes (Details) - USD ($) $ in Thousands							3 Months Ended		12 Months Ended
	Aug. 20, 2018	Jul. 16, 2018	Sep. 12, 2016	May 21, 2015	Nov. 17, 2014	May 20, 2013	Sep. 30, 2018	Mar. 31, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Senior Notes [Line Items]
Principal amount, net of unamortized deferred financing costs									$ 2,453,035	$ 2,448,439
Loss on extinguishment of debt									0	(26,740)	$ (35)
Accelerated unamortized deferred financing costs for extinguishment of debt									$ 0	6,334	$ 22
6.125% Senior Notes Due 2022 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage									6.125%
Principal amount					$ 600,000				$ 476,796	476,796
Unamortized deferred financing costs									(2,920)	(3,921)
Principal amount, net of unamortized deferred financing costs									$ 473,876	472,875
Senior Notes, repurchased face amount							$ 85,000	$ 38,200
Senior Notes repurchased, settlement amount							89,500	$ 24,300
Net proceeds from Senior Notes issuance					590,000
Senior Notes debt issuance costs					$ 10,000
5% Senior Notes Due 2024 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage									5.00%
Principal amount						$ 500,000			$ 500,000	500,000
Unamortized deferred financing costs									(3,766)	(4,688)
Principal amount, net of unamortized deferred financing costs									$ 496,234	495,312
Net proceeds from Senior Notes issuance						490,200
Senior Notes debt issuance costs						$ 9,800
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	500,000
Unamortized deferred financing costs									(4,903)	(5,808)
Principal amount, net of unamortized deferred financing costs									$ 495,097	494,192
Net proceeds from Senior Notes issuance				491,000
Senior Notes debt issuance costs				$ 9,000
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	500,000
Unamortized deferred financing costs									(5,571)	(6,407)
Principal amount, net of unamortized deferred financing costs									$ 494,429	493,593
Net proceeds from Senior Notes issuance			491,600
Senior Notes debt issuance costs			$ 8,400
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	500,000
Unamortized deferred financing costs									(6,601)	(7,533)
Principal amount, net of unamortized deferred financing costs									493,399	492,467
Net proceeds from Senior Notes issuance	492,100
Senior Notes debt issuance costs	$ 7,900
Senior Notes [Member]
Senior Notes [Line Items]
Principal amount									2,476,796	2,476,796
Unamortized deferred financing costs									(23,761)	(28,357)
Principal amount, net of unamortized deferred financing costs									$ 2,453,035	2,448,439
6.50% Senior Notes Due 2021 [Member]
Senior Notes [Line Items]
Senior Notes repurchased, settlement amount		$ 355,900
6.50% Senior Notes Due 2023 [Member]
Senior Notes [Line Items]
Senior Notes, repurchased face amount							395,000
Q3 2018 Senior Notes Transactions [Member]
Senior Notes [Line Items]
Senior Notes repurchased, settlement amount							$ 497,800
Loss on extinguishment of debt										(26,700)
Premiums paid for extinguishment of debt										20,400
Accelerated unamortized deferred financing costs for extinguishment of debt										$ 6,300