Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
		Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Cash Flows [Abstract]
Non-cash (gain) loss on extinguishment of debt, net					$ 0	$ 22
Loss on extinguishment of debt		$ 0		$ 0	0	35
Net cash provided by operating activities					311,518	242,128
Net cash provided by (used in) investing activities					(5,719)	311,364
Cash paid for extinguishment of debt					0	(13)
Net cash used in financing activities					(3,836)	(6,343)
Net change in cash, cash equivalents, and restricted cash						547,149
Cash, cash equivalents, and restricted cash at beginning of period	[1]		$ 313,943		313,943	12,372
Cash, cash equivalents, and restricted cash at end of period	[1]	615,906		559,521	615,906	559,521
Income Statement [Abstract]
Net income (loss)		17,197		(119,907)	334,598	(45,473)
Depreciation, depletion, amortization and asset retirement liability accretion expense		151,765		153,232	282,238	291,044
Exploration		14,056		12,983	27,783	24,800
General and administrative		28,920		28,237	56,602	57,054
Total operating expenses		387,768		268,047	698,295	474,624
Income (loss) from operations		56,148		(147,326)	515,216	18,835
Other non-operating income, net		1,802		953	$ 2,211	720
Scenario, Previously Reported [Member]
Statement of Cash Flows [Abstract]
Non-cash (gain) loss on extinguishment of debt, net						22
Net cash provided by operating activities						242,115
Other, net						3,000
Net cash provided by (used in) investing activities						314,364
Net cash used in financing activities						(6,330)
Net change in cash and cash equivalents						550,149
Cash and cash equivalents at beginning of period						9,372
Cash and cash equivalents at end of period				559,521		559,521
Income Statement [Abstract]
Exploration				13,072		25,050
General and administrative				28,460		57,684
Total operating expenses				268,359		475,504
Income (loss) from operations				(147,638)		17,955
Other non-operating income, net				$ 1,265		$ 1,600
Correction of Immaterial Errors Before Tax [Member]
Income Statement [Abstract]
Assets held for sale, loss (gain) on write-down		17,700
Depreciation, depletion, amortization and asset retirement liability accretion expense		6,700
Correction of Immaterial Errors After Tax [Member]
Income Statement [Abstract]
Assets held for sale, loss (gain) on write-down		13,700
Depreciation, depletion, amortization and asset retirement liability accretion expense		5,200
Overstatement of Net Income After Tax [Member]
Income Statement [Abstract]
Net income (loss)			$ 18,900
Understatement of Net Income After Tax [Member]
Income Statement [Abstract]
Net income (loss)		$ 18,900

[1] (1) Refer to Note 1 - Summary of Significant Accounting Policies for a reconciliation of cash, cash equivalents, and restricted cash reported to the amounts reported within the accompanying unaudited condensed consolidated balance sheets (“accompanying balance sheets”).