Long-Term Debt (Components of Long-Term Debt) (Details) - USD ($)	1 Months Ended
	Jan. 31, 2018	Dec. 31, 2017		May 31, 2016	Dec. 31, 2016	Apr. 30, 2014	Feb. 28, 2013	Feb. 28, 2011
Debt Instrument [Line Items]
Senior Secured Bank Credit Agreement		$ 475,000,000			$ 301,000,000
Senior Secured Second Lien Notes				$ 614,900,000
3 1/2% Convertible Senior Notes due 2024		84,650,000			0
Pipeline financings		192,429,000			202,671,000
Capital lease obligations		26,298,000			48,718,000
Total debt principal balance		2,775,391,000			2,779,914,000
Future interest payable		316,818,000	[1]		228,825,000
Debt issuance costs		(7,935,000)			(15,641,000)
Total debt, net of debt issuance costs		3,084,274,000			2,993,098,000
Less: current maturities of long-term debt		(105,188,000)	[1]		(83,366,000)
Long-term Debt and Capital Lease Obligations		2,979,086,000			2,909,732,000
Debt Instrument, Amount Exchanged		$ 609,800,000		$ 1,057,800,000
Subsequent Event
Debt Instrument [Line Items]
Debt Instrument, Amount Exchanged	$ 174,300,000
3 1/2% Convertible Senior Notes Due 2024
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.50%
Senior Secured and Convertible Senior Notes | Subsequent Event
Debt Instrument [Line Items]
Face value of notes	$ 133,500,000
5% Convertible Senior Notes Due 2023 | Subsequent Event
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.00%
Senior Subordinated Notes | 6 3/8% Senior Subordinated Notes due 2021
Debt Instrument [Line Items]
Senior Subordinated Notes		$ 215,144,000			215,144,000
Debt Instrument, Interest Rate, Stated Percentage		6.375%
Face value of notes								$ 400,000,000
Senior Subordinated Notes | 6 3/8% Senior Subordinated Notes due 2021 | Subsequent Event
Debt Instrument [Line Items]
Debt Instrument, Amount Exchanged	$ 11,600,000
Senior Subordinated Notes | 5 1/2% Senior Subordinated Notes due 2022
Debt Instrument [Line Items]
Senior Subordinated Notes		$ 408,882,000			772,912,000
Debt Instrument, Interest Rate, Stated Percentage		5.50%
Debt Instrument, Amount Exchanged		$ 364,000,000
Face value of notes						$ 1,250,000,000.00
Senior Subordinated Notes | 5 1/2% Senior Subordinated Notes due 2022 | Subsequent Event
Debt Instrument [Line Items]
Debt Instrument, Amount Exchanged	94,200,000
Senior Subordinated Notes | 4 5/8% Senior Subordinated Notes due 2023
Debt Instrument [Line Items]
Senior Subordinated Notes		$ 376,501,000			622,297,000
Debt Instrument, Interest Rate, Stated Percentage		4.625%
Debt Instrument, Amount Exchanged		$ 245,800,000
Face value of notes							$ 1,200,000,000.0
Senior Subordinated Notes | 4 5/8% Senior Subordinated Notes due 2023 | Subsequent Event
Debt Instrument [Line Items]
Debt Instrument, Amount Exchanged	68,500,000
Senior Subordinated Notes | Other Subordinated Notes
Debt Instrument [Line Items]
Senior Subordinated Notes		0			2,253,000
Including premium of		0			3,000
Secured Debt | 9% Senior Secured Second Lien Notes due 2021
Debt Instrument [Line Items]
Senior Secured Second Lien Notes		$ 614,919,000			614,919,000
Debt Instrument, Interest Rate, Stated Percentage		9.00%
Secured Debt | 9 1/4% Senior Secured Second Lien Notes Due 2022
Debt Instrument [Line Items]
Senior Secured Second Lien Notes		$ 381,568,000			0
Debt Instrument, Interest Rate, Stated Percentage		9.25%
Secured Debt | 9 1/4% Senior Secured Second Lien Notes Due 2022 | Subsequent Event
Debt Instrument [Line Items]
Face value of notes	$ 74,100,000
Future interest payable on senior secured and convertible senior notes
Debt Instrument [Line Items]
Less: current maturities of long-term debt		$ (75,347,000)			(50,349,000)
Long-term Debt and Capital Lease Obligations		$ 241,472,000			$ 178,476,000

[1] Future interest payable represents most of the interest due over the term of our 9% Senior Secured Second Lien Notes due 2021 (the “2021 Senior Secured Notes”), 9¼% Senior Secured Second Lien Notes due 2022 (the “2022 Senior Secured Notes”) and 3½% Convertible Senior Notes due 2024 (the “2024 Convertible Senior Notes”), which has been accounted for as debt in accordance with FASC 470-60, Troubled Debt Restructuring by Debtors. Our current maturities of long-term debt as of December 31, 2017 include $75.3 million of future interest payable related to these notes that is due within the next twelve months. See December 2017 and January 2018 Note Exchanges below for further discussion.