Supplemental Guarantor Information (Condensed Consolidating Statements of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Revenues	$ 539,331	$ 573,068	$ 535,548	$ 482,318	$ 497,043	$ 506,029	$ 470,068	$ 400,936	$ 2,130,265	$ 1,874,076	$ 1,450,047
Costs (exclusive of depreciation, depletion, amortization and accretion)	384,445	404,389	369,810	343,460	356,628	368,279	351,802	321,986	1,502,104	1,398,695	1,123,274
Depreciation, depletion, amortization and accretion	97,264	99,892	97,973	105,719	107,565	108,751	108,119	114,281	400,848	438,716	509,971
General and administrative expenses									289,252	295,507	346,606
Reduction in value of assets	739,725				4,202	9,953			739,725	14,155	500,405
Loss from operations									(801,664)	(272,997)	(1,030,209)
Other expense:
Interest expense, net									(99,477)	(101,455)	(92,753)
Other income (expense)									(1,678)	(3,299)	22,621
Loss from continuing operations before income taxes									(902,819)	(377,751)	(1,100,341)
Income taxes									(45,433)	(190,740)	(267,001)
Net loss from continuing operations	(750,185)	(21,816)	(25,437)	(59,948)	21,878	(57,189)	(62,039)	(89,661)	(857,386)	(187,011)	(833,340)
Loss from discontinued operations, net of income tax			(953)	224	(13,285)	(1,860)	(1,767)	(1,998)	(729)	(18,910)	(53,559)
Net loss	$ (750,185)	$ (21,816)	$ (26,390)	$ (59,724)	$ 8,593	$ (59,049)	$ (63,806)	$ (91,659)	(858,115)	(205,921)	(886,899)
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Revenues									(31,255)	(15,701)	(24,496)
Costs (exclusive of depreciation, depletion, amortization and accretion)									(31,255)	(15,701)	(24,496)
Other expense:
Equity in losses of consolidated subsidiaries									1,566,060	283,279	1,625,589
Loss from continuing operations before income taxes									1,566,060	283,279	1,625,589
Net loss from continuing operations									1,566,060	283,279	1,625,589
Net loss									1,566,060	283,279	1,625,589
Parent [Member]
Other expense:
Equity in losses of consolidated subsidiaries									(858,115)	(205,921)	(886,899)
Loss from continuing operations before income taxes									(858,115)	(205,921)	(886,899)
Net loss from continuing operations									(858,115)	(205,921)	(886,899)
Net loss									(858,115)	(205,921)	(886,899)
Issuer [Member]
Condensed Financial Statements, Captions [Line Items]
Costs (exclusive of depreciation, depletion, amortization and accretion)									(13,265)	(4,123)	6,582
Depreciation, depletion, amortization and accretion									3,945	4,149	4,592
General and administrative expenses									95,725	86,840	117,781
Loss from operations									(86,405)	(86,866)	(128,955)
Other expense:
Interest expense, net									(103,594)	(105,585)	(95,040)
Other income (expense)									71	(1,350)	(4,345)
Equity in losses of consolidated subsidiaries									(707,348)	(76,394)	(738,047)
Loss from continuing operations before income taxes									(897,276)	(270,195)	(966,387)
Income taxes									(39,161)	(64,274)	(79,488)
Net loss from continuing operations									(858,115)	(205,921)	(886,899)
Net loss									(858,115)	(205,921)	(886,899)
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Revenues									1,889,751	1,655,114	1,193,233
Costs (exclusive of depreciation, depletion, amortization and accretion)									1,355,524	1,242,486	944,349
Depreciation, depletion, amortization and accretion									351,974	383,713	452,180
General and administrative expenses									142,451	152,076	176,430
Reduction in value of assets									647,441	6,038	486,976
Loss from operations									(607,639)	(129,199)	(866,702)
Other expense:
Interest expense, net									3,950	4,451	3,425
Other income (expense)									1,014	202	196
Equity in losses of consolidated subsidiaries									(597)	(964)	(643)
Loss from continuing operations before income taxes									(603,272)	(125,510)	(863,724)
Income taxes									(6,554)	(118,347)	(189,850)
Net loss from continuing operations									(596,718)	(7,163)	(673,874)
Net loss									(596,718)	(7,163)	(673,874)
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Revenues									271,769	234,663	281,310
Costs (exclusive of depreciation, depletion, amortization and accretion)									191,100	176,033	196,839
Depreciation, depletion, amortization and accretion									44,929	50,854	53,199
General and administrative expenses									51,076	56,591	52,395
Reduction in value of assets									92,284	8,117	13,429
Loss from operations									(107,620)	(56,932)	(34,552)
Other expense:
Interest expense, net									167	(321)	(1,138)
Other income (expense)									(2,763)	(2,151)	26,770
Loss from continuing operations before income taxes									(110,216)	(59,404)	(8,920)
Income taxes									282	(8,119)	2,337
Net loss from continuing operations									(110,498)	(51,285)	(11,257)
Loss from discontinued operations, net of income tax									(729)	(18,910)	(53,559)
Net loss									$ (111,227)	$ (70,195)	$ (64,816)