Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Cash Flows [Abstract]
Non-cash (gain) loss on extinguishment of debt, net				$ 6,334	$ 22
Loss on extinguishment of debt		$ 26,722	$ 0	26,722	35
Net cash provided by operating activities				541,177	370,610
Net cash provided by (used in) investing activities				(313,960)	66,007
Cash paid for extinguishment of debt	[1]				13
Net cash used in financing activities				(364,354)	(7,574)
Net change in cash, cash equivalents, and restricted cash					429,043
Cash, cash equivalents, and restricted cash at beginning of period	[2]			313,943	12,372
Cash, cash equivalents, and restricted cash at end of period	[2]	176,806	441,415	176,806	441,415
Income Statement [Abstract]
Exploration		13,061	14,119	40,844	38,919
General and administrative		29,464	27,564	86,066	84,618
Total operating expenses		568,013	380,531	1,266,308	855,155
Income (loss) from operations		(108,644)	(85,152)	406,572	(66,317)
Other non-operating income, net		806	861	3,017	1,581
Prior Period Adjustments Restatement [Line Items]
Depletion, depreciation, amortization, and asset retirement obligation liability accretion		201,105	134,599	483,343	425,643
Net income (loss)		135,923	89,112	(198,675)	134,585
Previously Reported [Member] | Accounting Standards Update 2016-15, 2016-18 [Member]
Statement of Cash Flows [Abstract]
Non-cash (gain) loss on extinguishment of debt, net					22
Net cash provided by operating activities					370,597
Acquisition deposit held in escrow					3,000
Net cash provided by (used in) investing activities					69,007
Net cash used in financing activities					(7,561)
Net change in cash and cash equivalents					432,043
Cash and cash equivalents at beginning of period					9,372
Cash and cash equivalents at end of period			441,415		441,415
Previously Reported [Member] | Accounting Standards Update 2017-07 [Member]
Income Statement [Abstract]
Exploration			14,243		39,293
General and administrative			27,880		85,564
Total operating expenses			380,971		856,475
Income (loss) from operations			(85,592)		(67,637)
Other non-operating income, net			$ 1,301		$ 2,901
Correction of Immaterial Errors Before Tax [Member]
Prior Period Adjustments Restatement [Line Items]
Depletion, depreciation, amortization, and asset retirement obligation liability accretion		11,800		11,800
Understatement of Net Income After Tax [Member]
Prior Period Adjustments Restatement [Line Items]
Net income (loss)				$ 9,000
Overstatement of Net Loss After Tax [Member]
Prior Period Adjustments Restatement [Line Items]
Net income (loss)		$ 9,000

[1] (1) Included as a component within the cash paid to repurchase Senior Notes, including premium line item on the accompanying statements of cash flows.

[2] (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”).