Senior Notes(Details) - USD ($)						3 Months Ended	12 Months Ended
	May 21, 2015	Nov. 17, 2014	May 20, 2013	Jun. 29, 2012	Nov. 08, 2011	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2017	Sep. 12, 2016
Senior Notes [Line Items]
Senior Notes, net of unamortized deferred financing costs							$ 2,769,663,000	$ 2,766,719,000
Gain (loss) on extinguishment of debt							(35,000)	15,722,000	$ (16,578,000)
Loss on extinguishment of debt, acceleration of unamortized deferred financing costs							$ 22,000	(15,722,000)	4,123,000
6.50% Senior Notes Due 2021 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage							6.50%
Senior Notes, face amount					$ 350,000,000			346,955,000
Unamortized deferred financing costs							$ 2,656,000	3,372,000
Senior Notes, net of unamortized deferred financing costs							$ 341,955,000	343,583,000
Senior Notes, repurchased face amount						$ 3,100,000				$ 2,300,000
Senior Notes, repurchased settlement amount						2,300,000
Net proceeds from Senior Notes issuance					343,100,000
Senior Notes debt issuance costs, gross					$ (6,900,000)
6.125% Senior Notes Due 2022 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage							6.125%
Senior Notes, face amount		$ 600,000,000						561,796,000
Unamortized deferred financing costs							$ 5,800,000	6,979,000
Senior Notes, net of unamortized deferred financing costs							$ 555,996,000	554,817,000
Senior Notes, repurchased face amount						38,200,000
Senior Notes, repurchased settlement amount						24,300,000
Net proceeds from Senior Notes issuance		590,000,000
Senior Notes debt issuance costs, gross		$ (10,000,000)
6.50% Senior Notes Due 2023 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage							6.50%
Senior Notes, face amount				$ 400,000,000				394,985,000
Unamortized deferred financing costs							$ 3,707,000	4,436,000
Senior Notes, net of unamortized deferred financing costs							$ 391,278,000	390,549,000
Senior Notes, repurchased face amount						5,000,000
Senior Notes, repurchased settlement amount						3,300,000
Net proceeds from Senior Notes issuance				392,100,000
Senior Notes debt issuance costs, gross				$ (7,900,000)
5% Senior Notes Due 2024 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage							5.00%
Senior Notes, face amount			$ 500,000,000					500,000,000
Unamortized deferred financing costs							$ 5,610,000	6,533,000
Senior Notes, net of unamortized deferred financing costs							$ 494,390,000	493,467,000
Net proceeds from Senior Notes issuance			490,200,000
Senior Notes debt issuance costs, gross			$ (9,800,000)
5.625% Senior Notes Due 2025 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage							5.625%
Senior Notes, face amount	$ 500,000,000							500,000,000
Unamortized deferred financing costs							$ 6,714,000	7,619,000
Senior Notes, net of unamortized deferred financing costs							$ 493,286,000	492,381,000
Net proceeds from Senior Notes issuance	491,000,000
Senior Notes debt issuance costs, gross	$ (9,000,000)
6.75% Senior Notes Due 2026 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage							6.75%
Senior Notes, face amount								500,000,000			$ 500,000,000
Unamortized deferred financing costs							$ 7,242,000	8,078,000
Senior Notes, net of unamortized deferred financing costs							492,758,000	491,922,000
Net proceeds from Senior Notes issuance								491,600,000
Senior Notes debt issuance costs, gross											$ (8,400,000)
6.625% Senior Notes Due 2019 [Member]
Senior Notes [Line Items]
Gain (loss) on extinguishment of debt									(16,600,000)
Loss on extinguishment of debt, acceleration of unamortized deferred financing costs									(4,100,000)
Senior Notes, repurchase premium									$ 12,500,000
Senior Notes [Member]
Senior Notes [Line Items]
Senior Notes, face amount							2,801,392,000	2,803,736,000
Unamortized deferred financing costs							31,729,000	37,017,000
Senior Notes, net of unamortized deferred financing costs							2,769,663,000	2,766,719,000
Senior Notes, covenant compliance, dividends excluded from computation							$ 6,500,000
Senior Notes, repurchased face amount						46,300,000
Senior Notes, repurchased settlement amount						$ 29,900,000
Gain (loss) on extinguishment of debt								15,700,000
Senior Notes, repurchase discount								16,400,000
Loss on extinguishment of debt, acceleration of unamortized deferred financing costs								(700,000)
Senior Notes [Member] | 6.50% Senior Notes Due 2021 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage							6.50%
Senior Notes, face amount							$ 344,611,000	346,955,000
Senior Notes [Member] | 6.125% Senior Notes Due 2022 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage							6.125%
Senior Notes, face amount							$ 561,796,000	561,796,000
Senior Notes [Member] | 6.50% Senior Notes Due 2023 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage							6.50%
Senior Notes, face amount							$ 394,985,000	394,985,000
Senior Notes [Member] | 5% Senior Notes Due 2024 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage							5.00%
Senior Notes, face amount							$ 500,000,000	500,000,000
Senior Notes [Member] | 5.625% Senior Notes Due 2025 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage							5.625%
Senior Notes, face amount							$ 500,000,000	500,000,000
Senior Notes [Member] | 6.75% Senior Notes Due 2026 [Member]
Senior Notes [Line Items]
Senior Notes, interest rate, stated percentage							6.75%
Senior Notes, face amount							$ 500,000,000	$ 500,000,000