Warrior Met Coal (HCC) 10-Q 1 Aug 18 2018 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information Document - shares	6 Months Ended
	Jun. 30, 2018	Jul. 31, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	WARRIOR MET COAL, INC.
Entity Central Index key	1,691,303
Document Type	10-Q
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2,018
Amendment Flag	false
Document Fiscal Period Focus	Q2
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)		52,789,885

CONDENSED STATEMENTS OF OPERATI

CONDENSED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues:
Total revenues	$ 322,555,000	$ 363,370,000	$ 744,343,000	$ 617,334,000
Costs and expenses:
Cost of sales (exclusive of items shown separately below)	178,543,000	160,152,000	369,219,000	266,296,000
Cost of other revenues (exclusive of items shown separately below)	7,338,000	7,795,000	15,122,000	15,974,000
Depreciation and depletion	21,127,000	19,650,000	45,679,000	34,232,000
Selling, general and administrative	13,465,000	8,660,000	21,699,000	13,830,000
Transaction and other expenses	986,000	3,837,000	4,274,000	12,873,000
Total costs and expenses	221,459,000	200,094,000	455,993,000	343,205,000
Operating income	101,096,000	163,276,000	288,350,000	274,129,000
Interest expense, net	(9,784,000)	(642,000)	(18,344,000)	(1,250,000)
Income before income taxes	91,312,000	162,634,000	270,006,000	272,879,000
Income tax expense	0	32,769,000	0	34,706,000
Net income	$ 91,312,000	$ 129,865,000	$ 270,006,000	$ 238,173,000
Basic and diluted net income per share:
Net income (loss) per share—basic and diluted (in dollars per share)	$ 1.72	$ 2.46	$ 5.10	$ 4.52
Weighted average number of shares outstanding—basic (in shares)	53,053	52,721	52,976	52,702
Weighted average number of shares outstanding—diluted (in shares)	53,079	52,721	53,007	52,702
Dividends per share (in dollars per share)	$ 6.58	$ 0.05	$ 6.63	$ 3.61
Sales
Revenues:
Total revenues	$ 315,045,000	$ 351,788,000	$ 727,924,000
Other revenues
Revenues:
Total revenues	$ 7,510,000	$ 11,582,000	$ 16,419,000	$ 24,490,000

CONDENSED BALANCE SHEETS

CONDENSED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 55,087	$ 35,470
Short-term investments	17,501	17,501
Trade accounts receivable	129,946	117,746
Other receivables	10,274	14,482
Inventories, net	59,446	54,294
Prepaid expenses	20,750	29,376
Total current assets	293,004	268,869
Mineral interests, net	125,000	130,004
Property, plant and equipment, net	551,205	536,745
Income tax receivable	39,255	39,255
Other long-term assets	21,319	18,442
Total assets	1,029,783	993,315
Current liabilities:
Accounts payable	40,124	28,076
Accrued expenses	66,475	66,704
Other current liabilities	6,837	10,475
Current portion of long-term debt	2,257	2,965
Total current liabilities	115,693	108,220
Long-term debt	465,860	342,948
Asset retirement obligations	98,282	96,096
Other long-term liabilities	35,078	33,028
Total liabilities	714,913	580,292
Commitments and contingencies
Stockholders’ Equity:
Common stock, $0.01 par value per share (Authorized -140,000,000 shares, 53,287,079 issued and 52,787,079 outstanding as of June 30, 2018 and 53,284,470 issued and outstanding as of December 31, 2017)	534	534
Preferred stock, $0.01 par value per share (10,000,000 shares authorized, no shares issued and outstanding)	0	0
Treasury stock, at cost	(12,100)	0
Additional paid in capital	238,162	329,993
Retained earnings	88,274	82,496
Total stockholders’ equity	314,870	413,023
Total liabilities and stockholders’ equity	$ 1,029,783	$ 993,315

CONDENSED BALANCE SHEETS CONDEN

CONDENSED BALANCE SHEETS CONDENSED BALANCE SHEETS (Parenthetical) - $ / shares	Jun. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Common stock par value (in dollars per share)	$ 0.01	$ 0.01
Common stock shares authorized (in shares)	140,000,000	140,000,000
Common stock shares issued (in shares)	53,287,079	53,284,470
Common stock shares outstanding (in shares)	52,787,079	53,284,470
Preferred stock par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock shares authorized (in shares)	10,000,000	10,000,000
Preferred stock shares issued (in shares)	0	0
Preferred stock shares outstanding (in shares)	0	0

CONDENSED STATEMENT OF CHANGES

CONDENSED STATEMENT OF CHANGES IN STOCKHOLDERS’ EQUITY - 6 months ended Jun. 30, 2018 - USD ($) $ in Thousands	Total	Common Stock	Preferred Stock	Treasury Stock	Additional Paid in Capital	Retained Earnings
Balance at beginning of period at Dec. 31, 2017	$ 413,023	$ 534	$ 0	$ 0	$ 329,993	$ 82,496
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	270,006					270,006
Dividends paid ($6.63 per share)	(355,350)				(91,122)	(264,228)
Stock compensation	4,679				4,679
Treasury stock purchase	(12,100)			(12,100)
Other	(5,388)				(5,388)
Balance at end of period at Jun. 30, 2018	$ 314,870	$ 534	$ 0	$ (12,100)	$ 238,162	$ 88,274

CONDENSED STATEMENT OF CHANGES6

CONDENSED STATEMENT OF CHANGES IN STOCKHOLDERS’ EQUITY (Parenthetical) - $ / shares	Apr. 20, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Stockholders' Equity [Abstract]
Dividends per share (in dollars per share)	$ 6.53	$ 6.58	$ 0.05	$ 6.63	$ 3.61

CONDENSED STATEMENTS OF CASH FL

CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
OPERATING ACTIVITIES
Net income	$ 270,006	$ 238,173
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and depletion	45,679	34,232
Stock based compensation expense	4,679	922
Amortization of debt issuance costs and debt discount/premium, net	1,396	889
Accretion of asset retirement obligations	2,310	1,899
Changes in operating assets and liabilities:
Trade accounts receivable	(12,200)	(26,655)
Other receivables	4,208	1,200
Inventories	(5,390)	(32,931)
Prepaid expenses	8,626	(4,674)
Accounts payable	15,469	7,778
Accrued expenses and other current liabilities	(3,723)	10,017
Other	(4,803)	(3,893)
Net cash provided by operating activities	326,257	226,957
INVESTING ACTIVITIES
Purchase of property, plant and equipment	(55,419)	(28,263)
Net cash used in investing activities	(55,419)	(28,263)
FINANCING ACTIVITIES
Dividends paid	(355,350)	(192,673)
Proceeds from issuance of debt	126,875	0
Retirements of debt	(1,513)	(1,531)
Debt issuance costs paid	(3,713)	0
Common shares repurchased	(12,100)	0
Other	(5,388)	0
Net cash used in financing activities	(251,189)	(194,204)
Net increase in cash and cash equivalents and restricted cash	19,649	4,490
Cash and cash equivalents and restricted cash at beginning of period	36,264	152,656
Cash and cash equivalents and restricted cash at end of period	$ 55,913	$ 157,146

Business and Basis of Presentat

Business and Basis of Presentation	6 Months Ended
	Jun. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business and Basis of Presentation	Business and Basis of Presentation Description of the Business Warrior Met Coal, LLC (the “Company”) was formed on September 3, 2015 by certain Walter Energy, Inc. (“Walter Energy”) lenders under the 2011 Credit Agreement, dated as of April 1, 2011, and the noteholders under the 9.50% Senior Secured Notes due 2019 in connection with the acquisition by the Company of certain core operating assets of Walter Energy (the "Asset Acquisition") under section 363 under Chapter 11 of Title 11 of the U.S. Bankruptcy Code in the Northern District of Alabama, Southern Division (the "Bankruptcy Court"). On January 8, 2016, the Bankruptcy Court approved the Asset Acquisition, which closed on March 31, 2016. The Company is a U.S. based producer and exporter of metallurgical (“met”) coal for a diversified customer base of blast furnace steel producers located primarily in Europe, South America and Asia. The Company also generates ancillary revenues from the sale of natural gas extracted as a byproduct from the underground coal mines and royalty revenues from leased properties. Corporate Conversion and Initial Public Offering On April 12, 2017, in connection with the Company’s initial public offering (“IPO”), Warrior Met Coal, LLC filed a certificate of conversion, whereby Warrior Met Coal, LLC effected a corporate conversion from a Delaware limited liability company to a Delaware corporation and changed its name to Warrior Met Coal, Inc. In connection with this corporate conversion, the Company filed a certificate of incorporation. Pursuant to the Company’s certificate of incorporation, the Company is authorized to issue up to 140,000,000 shares of common stock $ 0.01 par value per share and 10,000,000 shares of preferred stock $ 0.01 par value per share. All references in the unaudited interim condensed financial statements to the number of shares and per share amounts of common stock have been retroactively recast to reflect the corporate conversion. On April 19, 2017, the Company completed its IPO whereby the selling stockholders named in the Registration Statement on Form S-1 (File No. 333-216499) sold 16,666,667 shares of common stock at a price to the public of $ 19.00 per share. The Company did not receive any proceeds from the sale of common stock in the IPO. All of the net proceeds from the IPO were received by the selling stockholders. The aggregate net proceeds to the selling stockholders in the IPO were $296.9 million , net of underwriting discounts and commissions of $19.8 million . The Company has paid cumulative offering expenses of $15.9 million on behalf of the selling stockholders. Upon the closing of the IPO, 53,442,532 shares of common stock were outstanding. On April 13, 2017, our common stock began trading on the New York Stock Exchange under the ticker symbol "HCC" and on April 19, 2017, we closed our IPO. Basis of Presentation The accompanying financial statements are presented in accordance with accounting principles generally accepted in the United States (“GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. In our opinion the financial statements include all adjustments (consisting of normal recurring accruals) necessary in order to make the financial statements not misleading. Operating results for the three and six months ended June 30, 2018 and June 30, 2017 are not necessarily indicative of the final results that may be expected for the year ended December 31, 2018 . The balance sheet at December 31, 2017 has been derived from the audited consolidated financial statements for the year ended December 31, 2017 included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017 (the "2017 Annual Report").

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Our significant accounting policies are consistent with those disclosed in Note 2 to our audited financial statements included in the 2017 Annual Report, except for changes related to new accounting pronouncements described below. Cash and Cash Equivalents and Restricted Cash The following table provides a reconciliation of cash and cash equivalents and restricted cash reported within the Condensed Balance Sheets that sum to the total of the same such amounts shown in the Condensed Statements of Cash Flows (in thousands): June 30, 2018 December 31, 2017 Cash and cash equivalents $ 55,087 $ 35,470 Restricted cash included in other long-term assets 826 794 Total cash and cash equivalents and restricted cash included in the Statements of Cash Flows $ 55,913 $ 36,264 Cash and cash equivalents include short-term deposits and highly liquid investments that have original maturities of three months or less when purchased and are stated at cost, which approximates fair value. As of June 30, 2018 , restricted cash included in other long-term assets in the Condensed Balance Sheet represents amounts invested in certificate of deposits as financial assurance for post mining reclamation obligations. As of December 31, 2017 , restricted cash included in other long-term assets in the Condensed Balance Sheet represents amounts funded to an escrow account as collateral for coal royalties due under certain underground coal mining lease contracts. Short-Term Investments Instruments with maturities greater than three months, but less than twelve months, are included in short-term investments. The Company purchases United States Treasury bills with maturities ranging from six to twelve months which are classified as held to maturity and are carried at amortized cost, which approximates fair value. Securities classified as held to maturity securities are those securities that management has the intent and ability to hold to maturity. As of June 30, 2018 and December 31, 2017 , the Company’s short-term investments consisted of $17.5 million in Treasury bills with a maturity of six months . These Treasury bills were posted as collateral for the self-insured black lung related claims asserted by or on behalf of former employees of Walter Energy and its subsidiaries, which were assumed in the Asset Acquisition and relate to periods prior to March 31, 2016. Revenue Recognition The Company adopted Accounting Standards Update (“ASU”) No. 2014-09, “Revenue from Contracts with Customers”, as of January 1, 2018, using the modified retrospective approach. The Company will apply the standard to all customer contracts entered into as of the date of initial application. The Company has concluded that the adoption did not change the timing at which the Company has historically recognized revenue nor did it have a material impact on its consolidated financial statements. For periods prior to January 1, 2018, revenue is recognized when the following criteria have been met: (i) persuasive evidence of an arrangement exists; (ii) the price to the buyer is fixed or determinable; (iii) delivery has occurred; and (iv) collectability is reasonably assured. Delivery is considered to have occurred at the time title and risk of loss transfers to the customer. For coal shipments to domestic customers via rail, delivery occurs when the railcar is loaded. For coal shipments to international customers via ocean vessel, delivery occurs when the vessel is loaded at the Port of Mobile, Alabama. For natural gas sales, delivery occurs when the gas has been transferred to the pipeline. For periods subsequent to January 1, 2018, revenue is recognized when performance obligations under the terms of a contract with our customers are satisfied; for all contracts this occurs when control of the promised goods have been transferred to our customers. For coal shipments to domestic customers via rail, control is transferred when the railcar is loaded. For coal shipments to international customers via ocean vessel, control is transferred when the vessel is loaded at the Port of Mobile, Alabama. For natural gas sales, control is transferred when the gas has been transferred to the pipeline. Revenue is disaggregated between coal sales within the Company's mining segment and natural gas sales included in all other revenues, as disclosed in Note 12. For the three months ended June 30, 2018, our geographic customer mix was 63% in Europe, 24% in South America and 13% in Asia. For the three months ended June 30, 2017, our geographic customer mix was 67% in Europe, 21% in South America and 12% in Asia. For the six months ended June 30, 2018, our geographic customer mix was 55% in Europe, 25% in South America and 20% in Asia. For the six months ended June 30, 2017, our geographic customer mix was 70% in Europe, 17% in South America and 13% in Asia. Since February 2017, we have had an arrangement with XCoal Energy & Resource ("XCoal") to serve as XCoal's strategic partner for exports of low-volatility HCC. Under this arrangement, XCoal takes title to and markets coal that we would historically have sold on the spot market, in an amount of the greater of (i) 10% of our total production during the applicable term of the arrangement or (ii) 250,000 metric tons. During the three months ended June 30, 2018 and 2017, XCoal accounted for approximately $42.2 million , or 13% of total revenues, and $74.7 million , or 21% of total revenues, respectively. During the six months ended June 30, 2018 and 2017, XCoal accounted for approximately $144.9 million , or 19% of total revenues, and $90.0 million , or 15% of total revenues, respectively. New Accounting Pronouncements In February 2016, the Financial Accounting Standards Board ("FASB") issued ASU No. 2016-02, "Leases (Topic 842)". ASU 2016-02 contains accounting guidance that will require a lessee to recognize a right of use asset and lease liability on the balance sheet for all leases, with the exception of short-term leases. Additional qualitative disclosures along with specific quantitative disclosures will also be required. The Company plans to adopt this standard on January 1, 2019. The Company is currently evaluating whether this standard will have a material impact on the Company's consolidated financial position and results of operations.

Inventories, net

Inventories, net	6 Months Ended
	Jun. 30, 2018
Inventory Disclosure [Abstract]
Inventories, net	Inventories, net Inventories, net are summarized as follows (in thousands): June 30, 2018 December 31, 2017 Coal $ 37,221 $ 32,422 Raw materials, parts, supplies and other, net 22,225 21,872 Total inventories, net $ 59,446 $ 54,294

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes For the three and six months ended June 30, 2018 , the Company estimated its annual effective tax rate and applied this effective tax rate to its year-to-date pretax income at the end of the interim reporting period. The tax effect of unusual or infrequently occurring items, including effects of changes in tax laws or rates and changes in judgment about the realizability of deferred tax assets, are reported in the interim period in which they occur. The Company had no income tax expense for the three and six months ended June 30, 2018 due to the utilization of NOLs to offset taxable income. The Company recognized income tax expense of $ 32.8 million and $34.7 million for the three and six months ended June 30, 2017 , respectively.

Debt

Debt	6 Months Ended
	Jun. 30, 2018
Debt Disclosure [Abstract]
Debt	Debt Debt consisted of the following (in thousands): June 30, 2018 December 31, 2017 Weighted Average Interest Rate at June 30, 2018 Final Maturity Senior secured notes $ 475,000 $ 350,000 8% 2024 Promissory note 2,257 3,725 4% 2019 Debt discount/premium, net (9,140 ) (7,812 ) Total debt 468,117 345,913 Less: current debt (2,257 ) (2,965 ) Total long-term debt $ 465,860 $ 342,948 The Company's minimum debt repayment schedule, excluding interest, as of June 30, 2018 is as follows (in thousands): Payments Due 2018 2019 2020 2021 2022 Thereafter Senior secured notes $ — $ — $ — $ — $ — $475,000 Promissory note 1,497 760 — — — — Total $ 1,497 $ 760 $ — $ — $ — $ 475,000 Senior Secured Notes On March 1, 2018, the Company issued $125.0 million in aggregate principal amount of its 8.00% Senior Secured Notes due 2024 to qualified institutional buyers pursuant to Rule 144A under the Securities Act of 1933, as amended (the "Securities Act"), and to certain non-U.S. persons in transactions outside the United States in accordance with Regulation S under the Securities Act ("Regulation S"). The New Notes were issued at 103.00% of the aggregate principal amount thereof, plus accrued interest from November 2, 2017. The New Notes were issued as "Additional Notes" under the indenture dated as of November 2, 2017 (the "Original Indenture") among the Company, the subsidiary guarantors party thereto and Wilmington Trust, National Association, as trustee (the "Trustee") and priority lien collateral trustee (the "Priority Lien Collateral Trustee"), as supplemented by the First Supplemental Indenture, dated as of March 1, 2018 (the "First Supplemental Indenture" and, the Original Indenture as supplemented thereby, the "Indenture"). The New Notes have not been and will not be registered under the Securities Act, and may not be offered or sold in the United States absent registration or an applicable exemption from the registration requirements of the Securities Act. In connection with the issuance of the $125.0 million senior secured notes, the Company incurred transaction costs of approximately $3.3 million , which consists of legal fees and structuring fees, and is included in transaction and other expenses in the Condensed Statements of Operations. In addition, the Company incurred debt issuance costs of approximately $3.7 million , which consists of consent solicitation fees paid to holders of the Existing Notes (as defined below), and is included in long-term debt in the Condensed Balance Sheet. The New Notes and the $350.0 million in aggregate principal amount of the Company’s existing 8.00% Senior Secured Notes due 2024 (the “Existing Notes”), which were issued under the Original Indenture on November 2, 2017, rank pari passu in right of payment and constitute a single class of securities for all purposes under the Indenture, including, without limitation, waivers, amendments, redemptions, offers to purchase and collateral matters, and are fungible (except that the New Notes issued pursuant to Regulation S traded separately under different CUSIP/ISIN numbers until 40 days after the issue date, but thereafter any such holders may transfer their New Notes pursuant to Regulation S into the same CUSIP/ISIN numbers as the Existing Notes issued pursuant to Regulation S). The Notes will mature on November 1, 2024 and interest is payable on May 1 and November 1 of each year, commencing on May 1, 2018. The Company used the net proceeds of the offering of the $125.0 million senior secured notes, together with cash on hand of $225.0 million , to pay a special dividend of approximately $350.0 million , or $6.53 per share, to all of its stockholders on a pro rata basis on April 20, 2018 (the "April Special Dividend").

Net Income per Share

Net Income per Share	6 Months Ended
	Jun. 30, 2018
Earnings Per Share [Abstract]
Net Income per Share	Net Income per Share Basic and diluted net income per share was calculated as follows (in thousands, except per share data): For the three months ended For the six months ended 2018 2017 2018 2017 Numerator: Net income $ 91,312 $ 129,865 $ 270,006 $ 238,173 Denominator: Weighted-average shares used to compute net income per share—basic 53,053 52,721 52,976 52,702 Dilutive restrictive stock awards 26 — 31 — Weighted-average shares used to compute net income per share—diluted 53,079 52,721 53,007 52,702 Net income per share—basic and diluted $ 1.72 $ 2.46 $ 5.10 $ 4.52 On March 5, 2018, the Company awarded 186,916 restricted stock unit awards under the Company's 2017 Equity Incentive Plan (the "2017 Equity Plan"). These awards have certain service-based, performance-based and market-based vesting conditions and vest over a period of three years. The Company recognized approximately $0.6 million and $0.8 million in stock compensation expense associated with these awards for the three and six months ended June 30, 2018 , respectively. As of June 30, 2018, neither the service, performance nor market-based vesting conditions were met as of the measurement date and as such have been excluded from basic and diluted earnings per share. As of June 30, 2018 , there were 152,807 shares of common stock issued and outstanding under the Company's 2016 Equity Incentive Plan (the "2016 Equity Plan") to certain directors and employees, for which the service vesting condition was not met as of the measurement date. During the second quarter of 2018, certain stockholders of the Company sold in two separate transactions an aggregate of 13,000,000 shares of the Company's common stock in a public secondary offerings (see Note 9). In connection with the first of these secondary offerings, a performance-based vesting condition was met resulting in approximately $3.6 million of incremental stock compensation expense. As of June 30, 2018 , there were 43,580 shares of our common stock contingently issuable upon the settlement of a vested phantom unit award under our 2016 Equity Plan and 13,157 shares of our common stock contingently issuable upon the settlement of a vested restricted stock unit award under our 2017 Equity Plan. The settlement date is the earlier of a change in control as described in our 2016 Equity Plan and 2017 Equity Plan or five years from the grant date. These awards are vested and as such have been included in the weighted-average shares used to compute basic and diluted net income per share. As of June 30, 2018 , there were 99,829 vested shares of common stock and 205,566 unvested awards issued under the 2017 Equity Plan to certain directors and employees.

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2018
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions In connection with the Asset Acquisition, the Company acquired a 50% interest in Black Warrior Methane (“BWM”) and Black Warrior Transmission (“BWT”), which are accounted for under the proportionate consolidation method and equity method, respectively. The Company has granted the rights to produce and sell methane gas from its coal mines to BWM and BWT. The Company’s net investments in, advances to/from BWT and equity in earnings or loss of BWT are not material to the Company. The Company supplied labor to BWM and incurred costs, including property and liability insurance, to support the joint venture. The Company charged the joint venture for such costs on a monthly basis, which were $0.7 million and $1.5 million for the three and six months ended June 30, 2018 , respectively, and $0.1 million and $0.8 million for the three and six months ended June 30, 2017 , respectively.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Environmental Matters The Company is subject to a wide variety of laws and regulations concerning the protection of the environment, both with respect to the construction and operation of its plants, mines and other facilities and with respect to remediating environmental conditions that may exist at its own and other properties. The Company believes that it is in substantial compliance with federal, state and local environmental laws and regulations. The Company accrues for environmental expenses resulting from existing conditions that relate to past operations when the costs are probable and can be reasonably estimated. As of June 30, 2018 and December 31, 2017 , there were no accruals for environmental matters other than asset retirement obligations for mine reclamation. Miscellaneous Litigation From time to time, the Company is party to a number of lawsuits arising in the ordinary course of their businesses. The Company records costs relating to these matters when a loss is probable and the amount can be reasonably estimated. The effect of the outcome of these matters on the Company’s future results of operations cannot be predicted with certainty as any such effect depends on future results of operations and the amount and timing of the resolution of such matters. As of June 30, 2018 and December 31, 2017 , there were no items accrued for miscellaneous litigation. Commitments and Contingencies—Other The Company is party to various transportation and throughput agreements with rail and barge transportation providers and the Alabama State Port Authority. These agreements contain annual minimum tonnage guarantees with respect to coal transported from the mine sites to the Port of Mobile, Alabama, unloading of rail cars or barges, and the loading of vessels. If the Company does not meet its minimum throughput obligations, which are based on annual minimum amounts, it is required to pay the transportation providers or the Alabama State Port Authority a contractually specified amount per metric ton for the difference between the actual throughput and the minimum throughput requirement. At June 30, 2018 and December 31, 2017 , the Company had no liability recorded for minimum throughput requirements. Royalty and Lease Obligations The Company’s leases are primarily for mining equipment and automobiles. At June 30, 2018 and December 31, 2017 , the Company had no future minimum payments due under non-cancellable operating leases. A substantial amount of the coal that the Company mines is produced from mineral reserves leased from third-party land owners. These leases convey mining rights to the Company in exchange for royalties to be paid to the land owner as either a fixed amount per ton or as a percentage of the sales price. Although coal leases have varying renewal terms and conditions, they generally last for the economic life of the reserves. Coal royalty expense was $23.3 million and $54.2 million for the three and six months ended June 30, 2018 , respectively, and $30.7 million and $52.2 million for the three and six months ended June 30, 2017 , respectively.

Stockholders' Equity

Stockholders' Equity	6 Months Ended
	Jun. 30, 2018
Equity [Abstract]
Stockholders' Equity	Stockholders' Equity Pursuant to the Company's certificate of incorporation, the Company is authorized to issue up to 140,000,000 shares of common stock $0.01 par value per share and 10,000,000 shares of preferred stock $0.01 par value per share. On March 31, 2017, the board of managers declared a cash distribution payable to holders of our then outstanding Class A Units, Class B Units and Class C Units as of March 27, 2017, resulting in distributions to such holders in the aggregate amount of $190.0 million (the “March Special Distribution”). In connection with the conversion of Warrior Met Coal, LLC into Warrior Met Coal, Inc., the Class C Units, which were issued pursuant to the 2016 Equity Plan, were converted into restricted shares (the "Restricted Shares") of common stock of the Company, par value $0.01 per share, and the March Special Distribution with respect to such Restricted Shares was not paid but held in trust pending their vesting. As of June 30, 2018 , approximately $5.7 million is held in the trust and is included within other long-term assets in the accompanying Condensed Balance Sheets. Stock Repurchase Program On May 2, 2018, the Board approved a stock repurchase program (the “Stock Repurchase Program”) that authorizes repurchases of up to an aggregate of $40.0 million of the Company's outstanding common stock. The Stock Repurchase Program does not require the Company to repurchase a specific number of shares or have an expiration date. The Stock Repurchase Program may be suspended or discontinued by the Board at any time without prior notice. Under the Stock Repurchase Program, the Company may repurchase shares of its common stock from time to time, in amounts, at prices and at such times as the Company deems appropriate, subject to market and industry conditions, share price, regulatory requirements as determined from time to time by the Company and other considerations. The Company’s repurchases may be executed using open market purchases or privately negotiated transactions in accordance with applicable securities laws and regulations, including Rule 10b-18 of the Exchange Act and repurchases may be executed pursuant to Rule 10b5-1 under the Exchange Act. Repurchases will be subject to limitations in the ABL Facility and the Indenture. The Company intends to fund repurchases under the Stock Repurchase Program from cash on hand and/or other sources of liquidity. Secondary Equity Offerings On May 10, 2018 certain stockholders of the Company sold 8,000,000 shares of the Company's common stock in a public secondary offering at a price to the underwriter of $24.20 per share. The Company did not receive any of the proceeds from this offering. In connection with this offering, the Company repurchased 500,000 shares of common stock under the Stock Repurchase Program, funded with cash on hand for the aggregate amount of $12.1 million (the "Stock Repurchase"). The shares repurchased by the Company in the Stock Repurchase are reflected as Treasury Stock on the Condensed Balance Sheets. On June 14, 2018, certain stockholders of the Company sold 5,000,000 shares of the Company's common stock in a public secondary offering at a price to the underwriter of $28.35 per share. The Company did not receive any of the proceeds from the offering. We refer to these two offerings herein as the "Secondary Equity Offerings."

Derivative Instruments

Derivative Instruments	6 Months Ended
	Jun. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	Derivative Instruments The Company enters into natural gas swap contracts to hedge the exposure to variability in expected future cash flows associated with the fluctuations in the price of natural gas related to the Company’s forecasted sales. As of June 30, 2018 and December 31, 2017 , the Company had natural gas swap contracts outstanding with notional amounts totaling 5,700 million and 8,400 million British thermal units, respectively, maturing in the first quarter of 2019, respectively. The Company’s natural gas swap contracts economically hedge certain risk but are not designated as hedges for financial reporting purposes. All changes in the fair value of these derivative instruments are recorded as other revenues in the Condensed Statements of Operations. The Company records all derivative instruments at fair value and had an asset of $0.3 million and $1.7 million related to natural gas swap contracts outstanding as of June 30, 2018 and December 31, 2017 , respectively, included in prepaid expenses in the accompanying Condensed Balance Sheets.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments The following table presents information about the Company’s financial liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands): Fair Value Measurements as of June 30, 2018 Using: Level 1 Level 2 Level 3 Total Assets: Natural gas swap contracts $ — $ 278 $ — $ 278 Fair Value Measurements as of December 31, 2017 Using: Level 1 Level 2 Level 3 Total Assets: Natural gas swap contracts $ — $ 1,644 $ — $ 1,644 The Company has no assets or any other liabilities measured at fair value on a recurring basis as of June 30, 2018 or December 31, 2017 . During the three and six months ended June 30, 2018 , there were no transfers between Level 1, Level 2 and Level 3. The Company uses quoted dealer prices for similar contracts in active over-the-counter markets for determining fair value of Level 2 liabilities. There were no changes to the valuation techniques used to measure liability fair values on a recurring basis during the three and six months ended June 30, 2018 . The following methods and assumptions were used to estimate the fair value for which the fair value option was not elected: Cash and cash equivalents, short-term investments, restricted cash, receivables and accounts payable— The carrying amounts reported in the Condensed Balance Sheet approximate fair value due to the short-term nature of these assets and liabilities. Debt— The Company's outstanding debt is carried at cost. As of June 30, 2018, there were no borrowings outstanding under the ABL Facility, with $95.4 million available, net of outstanding letters of credit of $4.6 million . There were no borrowings or outstanding letters of credit as of December 31, 2017. The estimated fair value of the Notes is approximately $491.6 million based upon observable market data (Level 2). The carrying value of the Company's outstanding promissory note approximates its fair value.

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 2018
Segment Reporting [Abstract]
Segment Information	Segment Information The Company identifies a business as an operating segment if: i) it engages in business activities from which it may earn revenues and incur expenses; ii) its operating results are regularly reviewed by the Chief Operating Decision Maker (“CODM”), who is the Company’s Chief Executive Officer, to make decisions about resources to be allocated to the segment and assess its performance; and iii) it has available discrete financial information. The Company has determined that its two underground mining operations are its operating segments. The CODM reviews financial information at the operating segment level to allocate resources and to assess the operating results and financial performance for each operating segment. Operating segments are aggregated into a reportable segment if the operating segments have similar quantitative economic characteristics and if the operating segments are similar in the following qualitative characteristics: i) nature of products and services; ii) nature of production processes; iii) type or class of customer for their products and services; iv) methods used to distribute the products or provide services; and v) if applicable, the nature of the regulatory environment. The Company has determined that the two operating segments are similar in both quantitative and qualitative characteristics and thus the two operating segments have been aggregated into one reportable segment. The Company has determined that its natural gas and royalty businesses did not meet the criteria in ASC 280 to be considered as operating or reportable segments. Therefore, the Company has included their results in an “all other” category as a reconciling item to consolidated amounts. The Company does not allocate all of its assets, or its depreciation and depletion expense, selling, general and administrative expenses, other post-retirement benefits, transactions costs, restructuring costs, interest expense, reorganization items, net and income tax expense by segment. The following tables include reconciliations of segment information to consolidated amounts (in thousands): For the three months ended For the six months ended June 30, 2018 2017 2018 2017 Revenues Mining $ 315,045 $ 351,788 $ 727,924 $ 592,844 All other 7,510 11,582 16,419 24,490 Total revenues $ 322,555 $ 363,370 $ 744,343 $ 617,334 For the three months ended For the six months ended June 30, 2018 2017 2018 2017 Capital Expenditures Mining 32,402 $ 16,093 $ 53,498 $ 26,586 All other 475 792 1,921 1,677 Total capital expenditures 32,877 $ 16,885 $ 55,419 $ 28,263 The Company evaluates the performance of its segment based on Segment Adjusted EBITDA, which is defined as net income adjusted for other revenues, cost of other revenues, depreciation and depletion, selling, general and administrative, net interest expense, income tax expense, and certain transactions or adjustments that the CODM does not consider for the purposes of making decisions to allocate resources among segments or assessing segment performance. Segment Adjusted EBITDA does not represent and should not be considered as an alternative to cost of sales under GAAP and may not be comparable to other similarly titled measures used by other companies. Below is a reconciliation of Segment Adjusted EBITDA to net income, which is its most directly comparable financial measure calculated and presented in accordance with GAAP (in thousands): For the three months ended For the six months ended June 30, 2018 2017 2018 2017 Segment Adjusted EBITDA $ 136,502 $ 191,636 $ 358,705 $ 326,548 Other revenues 7,510 11,582 16,419 24,490 Cost of other revenues (7,338 ) (7,795 ) (15,122 ) (15,974 ) Depreciation and depletion (21,127 ) (19,650 ) (45,679 ) (34,232 ) Selling, general and administrative (13,465 ) (8,660 ) (21,699 ) (13,830 ) Transaction and other expenses (986 ) (3,837 ) (4,274 ) (12,873 ) Interest expense, net (9,784 ) (642 ) (18,344 ) (1,250 ) Income tax expense — (32,769 ) — (34,706 ) Net income $ 91,312 $ 129,865 $ 270,006 $ 238,173

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Regular Quarterly Dividend On July 24, 2018, the Board declared a regular quarterly cash dividend of $0.05 per share, totaling approximately $2.7 million , which will be paid on August 10, 2018 to stockholders of record as of the close of business on August 3, 2018.

Summary of Significant Accoun21

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	The accompanying financial statements are presented in accordance with accounting principles generally accepted in the United States (“GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. In our opinion the financial statements include all adjustments (consisting of normal recurring accruals) necessary in order to make the financial statements not misleading.
Cash and Cash Equivalents and Restricted Cash	Cash and cash equivalents include short-term deposits and highly liquid investments that have original maturities of three months or less when purchased and are stated at cost, which approximates fair value. As of June 30, 2018 , restricted cash included in other long-term assets in the Condensed Balance Sheet represents amounts invested in certificate of deposits as financial assurance for post mining reclamation obligations. As of December 31, 2017 , restricted cash included in other long-term assets in the Condensed Balance Sheet represents amounts funded to an escrow account as collateral for coal royalties due under certain underground coal mining lease contracts.
Short-Term Investments	Short-Term Investments Instruments with maturities greater than three months, but less than twelve months, are included in short-term investments. The Company purchases United States Treasury bills with maturities ranging from six to twelve months which are classified as held to maturity and are carried at amortized cost, which approximates fair value. Securities classified as held to maturity securities are those securities that management has the intent and ability to hold to maturity.
Revenue Recognition and New Accounting Pronouncements	Revenue Recognition The Company adopted Accounting Standards Update (“ASU”) No. 2014-09, “Revenue from Contracts with Customers”, as of January 1, 2018, using the modified retrospective approach. The Company will apply the standard to all customer contracts entered into as of the date of initial application. The Company has concluded that the adoption did not change the timing at which the Company has historically recognized revenue nor did it have a material impact on its consolidated financial statements. For periods prior to January 1, 2018, revenue is recognized when the following criteria have been met: (i) persuasive evidence of an arrangement exists; (ii) the price to the buyer is fixed or determinable; (iii) delivery has occurred; and (iv) collectability is reasonably assured. Delivery is considered to have occurred at the time title and risk of loss transfers to the customer. For coal shipments to domestic customers via rail, delivery occurs when the railcar is loaded. For coal shipments to international customers via ocean vessel, delivery occurs when the vessel is loaded at the Port of Mobile, Alabama. For natural gas sales, delivery occurs when the gas has been transferred to the pipeline. For periods subsequent to January 1, 2018, revenue is recognized when performance obligations under the terms of a contract with our customers are satisfied; for all contracts this occurs when control of the promised goods have been transferred to our customers. For coal shipments to domestic customers via rail, control is transferred when the railcar is loaded. For coal shipments to international customers via ocean vessel, control is transferred when the vessel is loaded at the Port of Mobile, Alabama. For natural gas sales, control is transferred when the gas has been transferred to the pipeline. Revenue is disaggregated between coal sales within the Company's mining segment and natural gas sales included in all other revenues, as disclosed in Note 12. For the three months ended June 30, 2018, our geographic customer mix was 63% in Europe, 24% in South America and 13% in Asia. For the three months ended June 30, 2017, our geographic customer mix was 67% in Europe, 21% in South America and 12% in Asia. For the six months ended June 30, 2018, our geographic customer mix was 55% in Europe, 25% in South America and 20% in Asia. For the six months ended June 30, 2017, our geographic customer mix was 70% in Europe, 17% in South America and 13% in Asia. Since February 2017, we have had an arrangement with XCoal Energy & Resource ("XCoal") to serve as XCoal's strategic partner for exports of low-volatility HCC. Under this arrangement, XCoal takes title to and markets coal that we would historically have sold on the spot market, in an amount of the greater of (i) 10% of our total production during the applicable term of the arrangement or (ii) 250,000 metric tons. During the three months ended June 30, 2018 and 2017, XCoal accounted for approximately $42.2 million , or 13% of total revenues, and $74.7 million , or 21% of total revenues, respectively. During the six months ended June 30, 2018 and 2017, XCoal accounted for approximately $144.9 million , or 19% of total revenues, and $90.0 million , or 15% of total revenues, respectively. New Accounting Pronouncements In February 2016, the Financial Accounting Standards Board ("FASB") issued ASU No. 2016-02, "Leases (Topic 842)". ASU 2016-02 contains accounting guidance that will require a lessee to recognize a right of use asset and lease liability on the balance sheet for all leases, with the exception of short-term leases. Additional qualitative disclosures along with specific quantitative disclosures will also be required. The Company plans to adopt this standard on January 1, 2019. The Company is currently evaluating whether this standard will have a material impact on the Company's consolidated financial position and results of operations.

Summary of Significant Accoun22

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Schedule of Cash and Cash Equivalents	The following table provides a reconciliation of cash and cash equivalents and restricted cash reported within the Condensed Balance Sheets that sum to the total of the same such amounts shown in the Condensed Statements of Cash Flows (in thousands): June 30, 2018 December 31, 2017 Cash and cash equivalents $ 55,087 $ 35,470 Restricted cash included in other long-term assets 826 794 Total cash and cash equivalents and restricted cash included in the Statements of Cash Flows $ 55,913 $ 36,264
Schedule of Restricted Cash and Cash Equivalents	The following table provides a reconciliation of cash and cash equivalents and restricted cash reported within the Condensed Balance Sheets that sum to the total of the same such amounts shown in the Condensed Statements of Cash Flows (in thousands): June 30, 2018 December 31, 2017 Cash and cash equivalents $ 55,087 $ 35,470 Restricted cash included in other long-term assets 826 794 Total cash and cash equivalents and restricted cash included in the Statements of Cash Flows $ 55,913 $ 36,264

Inventories, net (Tables)

Inventories, net (Tables)	6 Months Ended
	Jun. 30, 2018
Inventory Disclosure [Abstract]
Schedule of Inventories, Net	Inventories, net are summarized as follows (in thousands): June 30, 2018 December 31, 2017 Coal $ 37,221 $ 32,422 Raw materials, parts, supplies and other, net 22,225 21,872 Total inventories, net $ 59,446 $ 54,294

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2018
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments	Debt consisted of the following (in thousands): June 30, 2018 December 31, 2017 Weighted Average Interest Rate at June 30, 2018 Final Maturity Senior secured notes $ 475,000 $ 350,000 8% 2024 Promissory note 2,257 3,725 4% 2019 Debt discount/premium, net (9,140 ) (7,812 ) Total debt 468,117 345,913 Less: current debt (2,257 ) (2,965 ) Total long-term debt $ 465,860 $ 342,948
Schedule of Maturities of Long-term Debt	The Company's minimum debt repayment schedule, excluding interest, as of June 30, 2018 is as follows (in thousands): Payments Due 2018 2019 2020 2021 2022 Thereafter Senior secured notes $ — $ — $ — $ — $ — $475,000 Promissory note 1,497 760 — — — — Total $ 1,497 $ 760 $ — $ — $ — $ 475,000

Net Income per Share (Tables)

Net Income per Share (Tables)	6 Months Ended
	Jun. 30, 2018
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	Basic and diluted net income per share was calculated as follows (in thousands, except per share data): For the three months ended For the six months ended 2018 2017 2018 2017 Numerator: Net income $ 91,312 $ 129,865 $ 270,006 $ 238,173 Denominator: Weighted-average shares used to compute net income per share—basic 53,053 52,721 52,976 52,702 Dilutive restrictive stock awards 26 — 31 — Weighted-average shares used to compute net income per share—diluted 53,079 52,721 53,007 52,702 Net income per share—basic and diluted $ 1.72 $ 2.46 $ 5.10 $ 4.52

Fair Value of Financial Instr26

Fair Value of Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value of Assets and Liabilities Measured on Recurring Basis	The following table presents information about the Company’s financial liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands): Fair Value Measurements as of June 30, 2018 Using: Level 1 Level 2 Level 3 Total Assets: Natural gas swap contracts $ — $ 278 $ — $ 278 Fair Value Measurements as of December 31, 2017 Using: Level 1 Level 2 Level 3 Total Assets: Natural gas swap contracts $ — $ 1,644 $ — $ 1,644

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 2018
Segment Reporting [Abstract]
Reconciliation of Revenue from Segments to Consolidated	The following tables include reconciliations of segment information to consolidated amounts (in thousands): For the three months ended For the six months ended June 30, 2018 2017 2018 2017 Revenues Mining $ 315,045 $ 351,788 $ 727,924 $ 592,844 All other 7,510 11,582 16,419 24,490 Total revenues $ 322,555 $ 363,370 $ 744,343 $ 617,334
Reconciliation of Capital Expenditures from Segments to Consolidated	For the three months ended For the six months ended June 30, 2018 2017 2018 2017 Capital Expenditures Mining 32,402 $ 16,093 $ 53,498 $ 26,586 All other 475 792 1,921 1,677 Total capital expenditures 32,877 $ 16,885 $ 55,419 $ 28,263
Reconciliation of Net Income (Loss) from Segments to Consolidated	Below is a reconciliation of Segment Adjusted EBITDA to net income, which is its most directly comparable financial measure calculated and presented in accordance with GAAP (in thousands): For the three months ended For the six months ended June 30, 2018 2017 2018 2017 Segment Adjusted EBITDA $ 136,502 $ 191,636 $ 358,705 $ 326,548 Other revenues 7,510 11,582 16,419 24,490 Cost of other revenues (7,338 ) (7,795 ) (15,122 ) (15,974 ) Depreciation and depletion (21,127 ) (19,650 ) (45,679 ) (34,232 ) Selling, general and administrative (13,465 ) (8,660 ) (21,699 ) (13,830 ) Transaction and other expenses (986 ) (3,837 ) (4,274 ) (12,873 ) Interest expense, net (9,784 ) (642 ) (18,344 ) (1,250 ) Income tax expense — (32,769 ) — (34,706 ) Net income $ 91,312 $ 129,865 $ 270,006 $ 238,173

Business and Basis of Present28

Business and Basis of Presentation - Description of the Business (Details)	Apr. 01, 2011
Walter Energy, Inc. | Senior secured notes | Senior Secured Notes due 2019
Business Acquisition [Line Items]
Stated interest rate	9.50%

Business and Basis of Present29

Business and Basis of Presentation - Corporate Conversion and Initial Public Offering (Details) - USD ($) $ / shares in Units, $ in Millions	Apr. 19, 2017	Jun. 30, 2018	Dec. 31, 2017	Apr. 12, 2017
Class of Stock [Line Items]
Common stock shares authorized (in shares)		140,000,000	140,000,000	140,000,000
Common stock par value (in dollars per share)		$ 0.01	$ 0.01	$ 0.01
Preferred stock shares authorized (in shares)		10,000,000	10,000,000	10,000,000
Preferred stock par value (in dollars per share)		$ 0.01	$ 0.01	$ 0.01
Common stock shares outstanding (in shares)		52,787,079	53,284,470
Common Stock | IPO
Class of Stock [Line Items]
Stock issued during period (in shares)	16,666,667
Shares issued (in dollars per share)	$ 19
Proceeds from issuance of common stock	$ 296.9
Stock issuance costs	19.8
Payments of stock issuance costs	$ 15.9
Common stock shares outstanding (in shares)	53,442,532

Summary of Significant Accoun30

Summary of Significant Accounting Policies - Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 55,087	$ 35,470
Restricted cash included in other long-term assets	826	794
Total cash and cash equivalents and restricted cash included in the Statements of Cash Flows	$ 55,913	$ 36,264	$ 157,146	$ 152,656

Summary of Significant Accoun31

Summary of Significant Accounting Policies - Short-Term Investments (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Short-term investments	$ 17,501	$ 17,501
Treasury bills
Schedule of Held-to-maturity Securities [Line Items]
Short-term investments	$ 17,500	$ 17,500
Maturity term for short-term investments	6 months	6 months

Summary of Significant Accoun32

Summary of Significant Accounting Policies - Revenue Recognition (Details) $ in Thousands	3 Months Ended		6 Months Ended		14 Months Ended
	Jun. 30, 2018USD ($)	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2018t
Concentration Risk [Line Items]
Percent of total production transferred for title and marketing					10.00%
Maximum total production transferred for title and marketing | t					250,000
Other revenues	$ 322,555	$ 363,370	$ 744,343	$ 617,334
Geographic Concentration Risk | Europe | Revenue
Concentration Risk [Line Items]
Concentration risk, percentage	63.00%	67.00%	55.00%	70.00%
Geographic Concentration Risk | South America | Revenue
Concentration Risk [Line Items]
Concentration risk, percentage	24.00%	21.00%	25.00%	17.00%
Geographic Concentration Risk | Asia | Revenue
Concentration Risk [Line Items]
Concentration risk, percentage	13.00%	12.00%	20.00%	13.00%
XCoal | Customer Concentration Risk | Revenue
Concentration Risk [Line Items]
Concentration risk, percentage	13.00%	21.00%	19.00%	15.00%
Other revenues	$ 42,200	$ 74,700	$ 144,900	$ 90,000

Inventories, net (Details)

Inventories, net (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Coal	$ 37,221	$ 32,422
Raw materials, parts, supplies and other, net	22,225	21,872
Total inventories, net	$ 59,446	$ 54,294

Income Taxes (Details)

Income Taxes (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Income tax expense	$ 0	$ 32,769,000	$ 0	$ 34,706,000

Debt - Schedule of Long-Term De

Debt - Schedule of Long-Term Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Debt discount/premium, net	$ (9,140)	$ (7,812)
Total debt	468,117	345,913
Less: current debt	(2,257)	(2,965)
Total long-term debt	465,860	342,948
Senior secured notes
Debt Instrument [Line Items]
Long-term debt, gross	475,000	$ 350,000
Weighted average interest rate		8.00%
Promissory note
Debt Instrument [Line Items]
Long-term debt, gross	$ 2,257	$ 3,725
Weighted average interest rate		4.00%

Debt - Debt Repayment Schedule

Debt - Debt Repayment Schedule (Details) $ in Thousands	Jun. 30, 2018USD ($)
Debt Instrument [Line Items]
2,018	$ 1,497
2,019	760
2,020	0
2,021	0
2,022	0
Thereafter	475,000
Senior secured notes
Debt Instrument [Line Items]
2,018	0
2,019	0
2,020	0
2,021	0
2,022	0
Thereafter	475,000
Promissory note
Debt Instrument [Line Items]
2,018	1,497
2,019	760
2,020	0
2,021	0
2,022	0
Thereafter	$ 0

Debt - Narrative (Details)

Debt - Narrative (Details) - USD ($)	Apr. 20, 2018	Mar. 01, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Debt Instrument [Line Items]
Debt issuance costs paid					$ 3,713,000	$ 0
Cash on hand to pay dividend	$ 225,000,000
Cash dividends	$ 350,000,000
Dividends per share (in dollars per share)	$ 6.53		$ 6.58	$ 0.05	$ 6.63	$ 3.61
Senior secured notes | Senior Secured Notes Due 2024, New Notes
Debt Instrument [Line Items]
Aggregate principal amount		$ 125,000,000
Stated interest rate		8.00%
Redemption price, percentage		103.00%
Transaction costs		$ 3,300,000
Debt issuance costs paid		$ (3,700,000)
Senior secured notes | Senior Secured Notes Due 2024, Existing Notes
Debt Instrument [Line Items]
Aggregate principal amount			$ 350,000,000		$ 350,000,000
Stated interest rate			8.00%		8.00%

Net Income per Share - Schedule

Net Income per Share - Schedule of Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net income	$ 91,312	$ 129,865	$ 270,006	$ 238,173
Denominator:
Weighted average number of shares outstanding—basic (in shares)	53,053	52,721	52,976	52,702
Dilutive restrictive stock awards	26	0	31	0
Weighted average number of shares outstanding—diluted (in shares)	53,079	52,721	53,007	52,702
Net income (loss) per share—basic and diluted (in dollars per share)	$ 1.72	$ 2.46	$ 5.10	$ 4.52

Net Income per Share - Narrativ

Net Income per Share - Narrative (Details) - USD ($) $ in Millions	Mar. 05, 2018	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Stock compensation expense		$ 0.6	$ 0.8
Common stock shares issued (in shares)		53,287,079	53,287,079	53,284,470
Common stock shares outstanding (in shares)		52,787,079	52,787,079	53,284,470
2016 Equity Plan
Class of Stock [Line Items]
Common stock shares issued (in shares)		152,807	152,807
Common stock shares outstanding (in shares)		152,807	152,807
Restricted Stock | 2017 Equity Plan
Class of Stock [Line Items]
Awards issued to employees and directors, unvested (in shares)		205,566	205,566
Phantom Share Units (PSUs) | 2016 and 2017 Equity Plans
Class of Stock [Line Items]
Settlement period			5 years
Phantom Share Units (PSUs) | 2016 Equity Plan
Class of Stock [Line Items]
Common stock shares contingently issuable (in shares)			43,580
Restricted Stock Units (RSUs) | 2017 Equity Plan
Class of Stock [Line Items]
Restricted stock unit awards awarded (in shares)	186,916
Common stock shares contingently issuable (in shares)			13,157
Common Stock | 2017 Equity Plan
Class of Stock [Line Items]
Common stock issued to employees and directors, vested (in shares)		99,829	99,829
Public Secondary Offering
Class of Stock [Line Items]
Incremental stock compensation expense		$ 3.6
Common Stock | Public Secondary Offering
Class of Stock [Line Items]
Stock issued during period (in shares)		13,000,000

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Nov. 05, 2015
Black Warrior Methane (BWM)
Related Party Transaction [Line Items]
Proportionate consolidation method, ownership percentage					50.00%
Black Warrior Transmission (BWT)
Related Party Transaction [Line Items]
Equity method investment, ownership percentage					50.00%
Allocated Expenses to Joint Venture | Corporate Joint Venture
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 0.7	$ 0.1	$ 1.5	$ 0.8

Commitments and Contingencies (

Commitments and Contingencies (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Throughput obligation	$ 0		$ 0		$ 0
Future minimum operating lease payments	0		0		$ 0
Coal royalty expense	$ 23,300,000	$ 30,700,000	$ 54,200,000	$ 52,200,000

Stockholders' Equity (Details)

Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions	Jun. 14, 2018	May 10, 2018	Mar. 31, 2017	Jun. 30, 2018	May 02, 2018	Dec. 31, 2017	Apr. 12, 2017
Class of Stock [Line Items]
Common stock shares authorized (in shares)				140,000,000		140,000,000	140,000,000
Common stock par value (in dollars per share)				$ 0.01		$ 0.01	$ 0.01
Preferred stock shares authorized (in shares)				10,000,000		10,000,000	10,000,000
Preferred stock par value (in dollars per share)				$ 0.01		$ 0.01	$ 0.01
Cash distributions paid			$ 190
Assets held in trust				$ 5.7
Restricted Stock
Class of Stock [Line Items]
Common stock par value (in dollars per share)				$ 0.01
The stock repurchase program
Class of Stock [Line Items]
Authorized amount of stock to be repurchased, value					$ 40
Shares repurchased (in shares)		500,000
Shares repurchased, value		$ 12.1
Public Secondary Offering
Class of Stock [Line Items]
Shares issued in second public offering (in shares)	5,000,000	8,000,000
Shares issued in second public offering (in dollars per share)	$ 28.35	$ 24.20

Derivative Instruments (Details

Derivative Instruments (Details) - Not Designated as Hedging Instrument - Natural gas swap contracts BTU in Millions, $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018USD ($)BTU	Dec. 31, 2017USD ($)BTU
Commodity Contract, Maturity Q4 2018
Derivative [Line Items]
Derivative energy measure (in BTUs) | BTU	5,700	8,400
Commodity Contract
Derivative [Line Items]
Natural gas swap contracts, asset	$ 0.3
Natural gas swap contracts, current liability		$ 1.7

Fair Value of Financial Instr44

Fair Value of Financial Instruments (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Letters of credit outstanding	$ 4,600,000	$ 0
Long-term debt	465,860,000	342,948,000
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on recurring basis	0	0
Fair Value, Measurements, Recurring | Commodity Contract | Natural gas swap contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Natural gas swap contracts, asset	278,000	1,644,000
Fair Value, Measurements, Recurring | Commodity Contract | Natural gas swap contracts | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Natural gas swap contracts, asset	0	0
Fair Value, Measurements, Recurring | Commodity Contract | Natural gas swap contracts | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Natural gas swap contracts, asset	278,000	1,644,000
Fair Value, Measurements, Recurring | Commodity Contract | Natural gas swap contracts | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Natural gas swap contracts, asset	0	0
ABL Facility | Revolving credit facility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount of borrowings available	95,400,000
Senior Secured Notes Due 2024, Existing Notes | Senior secured notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	0	$ 0
Senior Secured Notes Due 2024, Existing Notes | Senior secured notes | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of debt instrument	$ 491,600,000

Segment Information - Narrative

Segment Information - Narrative (Details)	6 Months Ended
	Jun. 30, 2018segment
Segment Reporting [Abstract]
Number of operating segments	2
Number of reportable segments	1

Segment Information - Reconcili

Segment Information - Reconciliation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Total revenues	$ 322,555	$ 363,370	$ 744,343	$ 617,334
Mining | Mining | Operating Segments
Segment Reporting Information [Line Items]
Total revenues	315,045	351,788	727,924	592,844
All other
Segment Reporting Information [Line Items]
Total revenues	7,510	11,582	16,419	24,490
All other | Segment Reconciling Items
Segment Reporting Information [Line Items]
Total revenues	$ 7,510	$ 11,582	$ 16,419	$ 24,490

Segment Information - Reconci47

Segment Information - Reconciliation of Capital Expenditures (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Capital Expenditures	$ 32,877	$ 16,885	$ 55,419	$ 28,263
Segment Reconciling Items
Segment Reporting Information [Line Items]
Capital Expenditures	475	792	1,921	1,677
Mining | Operating Segments
Segment Reporting Information [Line Items]
Capital Expenditures	$ 32,402	$ 16,093	$ 53,498	$ 26,586

Segment Information - Reconci48

Segment Information - Reconciliation of Net Income (Loss) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue from External Customer [Line Items]
Segment Adjusted EBITDA	$ 136,502,000	$ 191,636,000	$ 358,705,000	$ 326,548,000
Other revenues	322,555,000	363,370,000	744,343,000	617,334,000
Cost of other revenues	(7,338,000)	(7,795,000)	(15,122,000)	(15,974,000)
Depreciation and depletion	(21,127,000)	(19,650,000)	(45,679,000)	(34,232,000)
Selling, general and administrative	(13,465,000)	(8,660,000)	(21,699,000)	(13,830,000)
Transaction and other expenses	(986,000)	(3,837,000)	(4,274,000)	(12,873,000)
Interest expense, net	(9,784,000)	(642,000)	(18,344,000)	(1,250,000)
Income tax expense	0	(32,769,000)	0	(34,706,000)
Net income	91,312,000	129,865,000	270,006,000	238,173,000
Other revenues
Revenue from External Customer [Line Items]
Other revenues	$ 7,510,000	$ 11,582,000	$ 16,419,000	$ 24,490,000

Subsequent Events (Details)

Subsequent Events (Details) - Subsequent Event $ / shares in Units, $ in Millions	Jul. 24, 2018USD ($)$ / shares
Subsequent Event [Line Items]
Dividends declared (in dollars per share) | $ / shares	$ 0.05
Dividends Payable | $	$ 2.7