Long-term Debt Senior Notes (Details) - USD ($) $ in Thousands								3 Months Ended		12 Months Ended
	Aug. 20, 2018	Jul. 16, 2018	Jun. 15, 2018	Sep. 12, 2016	May 21, 2015	Nov. 17, 2014	May 20, 2013	Sep. 30, 2018	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Senior Notes [Line Items]
Principal amount, net of unamortized deferred financing costs										$ 2,448,439	$ 2,769,663
Gain (loss) on extinguishment of debt										(26,740)	(35)	$ 15,722
Loss on extinguishment of debt, acceleration of unamortized deferred financing costs										$ 6,334	22	(15,722)
6.50% Senior Notes Due 2021 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage										6.50%
Principal amount										$ 0	344,611
Unamortized deferred financing costs										0	(2,656)
Principal amount, net of unamortized deferred financing costs										0	341,955
Senior Notes, repurchased face amount			$ 344,611
Premiums paid for extinguishment of debt										7,500
Senior Notes repurchased, settlement amount		$ 355,900
Gain (loss) on extinguishment of debt										9,800
Loss on extinguishment of debt, acceleration of unamortized deferred financing costs										$ 2,300
Senior Notes, redemption price, percentage			102.167%
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	561,796
Unamortized deferred financing costs										(3,921)	(5,800)
Principal amount, net of unamortized deferred financing costs										$ 472,875	555,996
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
6.50% Senior Notes Due 2023 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage										6.50%
Principal amount										$ 0	394,985
Unamortized deferred financing costs										0	(3,707)
Principal amount, net of unamortized deferred financing costs										$ 0	391,278
Senior Notes, repurchased face amount								394,985	5,000
Senior Notes repurchased, settlement amount								408,300	3,300
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										(4,688)	(5,610)
Principal amount, net of unamortized deferred financing costs										$ 495,312	494,390
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										(5,808)	(6,714)
Principal amount, net of unamortized deferred financing costs										$ 494,192	493,286
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										(6,407)	(7,242)
Principal amount, net of unamortized deferred financing costs										$ 493,593	492,758
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	0
Unamortized deferred financing costs										(7,533)	0
Principal amount, net of unamortized deferred financing costs										492,467	0
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	2,801,392
Unamortized deferred financing costs										(28,357)	(31,729)
Principal amount, net of unamortized deferred financing costs										2,448,439	$ 2,769,663
Senior Notes, repurchased face amount									46,300
Senior Notes repurchased, settlement amount									$ 29,900
Gain (loss) on extinguishment of debt												15,700
Senior Notes repurchased, discount												16,400
Loss on extinguishment of debt, acceleration of unamortized deferred financing costs												$ 700
6.125% Senior Notes Due 2022 and 6.50% Senior Notes Due 2023 [Member]
Senior Notes [Line Items]
Premiums paid for extinguishment of debt										12,900
Senior Notes repurchased, settlement amount								$ 497,800
Gain (loss) on extinguishment of debt										16,900
Loss on extinguishment of debt, acceleration of unamortized deferred financing costs										$ 4,000