Warrior Met Coal (HCC) 10-K 21 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information Document - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 15, 2019	Jun. 30, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	WARRIOR MET COAL, INC.
Entity Central Index key	1,691,303
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Amendment Flag	false
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 1,200,000,000
Entity Common Stock, Shares Outstanding (in shares)		51,555,337

BALANCE SHEETS

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 205,577	$ 35,470
Short-term investments	17,501	17,501
Trade accounts receivable	138,399	117,746
Other receivables	1,434	5,306
Income tax receivable	21,607	9,176
Inventories, net	56,719	54,294
Prepaid expenses and other	27,932	29,376
Total current assets	469,169	268,869
Mineral interests, net	120,427	130,004
Property, plant and equipment, net	540,315	536,745
Non-current income tax receivable	21,310	39,255
Deferred income taxes	222,780	0
Other long-term assets	21,039	18,442
Total assets	1,395,040	993,315
Current liabilities:
Accounts payable	33,588	28,076
Accrued expenses	82,342	66,704
Asset retirement obligations	2,775	3,572
Other current liabilities	4,967	6,903
Current portion of long-term debt	760	2,965
Total current liabilities	124,432	108,220
Total long-term debt	468,231	342,948
Deferred income taxes	0	258
Asset retirement obligations	59,049	96,096
Black lung obligations	25,206	30,208
Other long-term liabilities	5,510	2,562
Total liabilities	682,428	580,292
Commitments and contingencies
Stockholders’ Equity:
Common stock, $0.01 par value per share (Authorized -140,000,000 shares, 53,256,098 issued and 51,622,898 outstanding as of December 31, 2018 and 53,284,470 issued and outstanding as of December 31, 2017)	533	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 (1,633,200 shares)	(38,030)	0
Additional paid in capital	239,827	329,993
Retained earnings	510,282	82,496
Total stockholders’ equity	712,612	413,023
Total liabilities and stockholders’ equity	$ 1,395,040	$ 993,315

BALANCE SHEETS (Parenthetical)

BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 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)	53,256,098	53,284,470
Common stock shares outstanding (in shares)	51,622,898	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
Treasury stock (in shares)	1,633,200,000	1,633,200,000

STATEMENTS OF OPERATIONS

STATEMENTS OF OPERATIONS - USD ($) shares in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Total revenues		$ 297,634,000	$ 1,378,007,000	$ 1,169,092,000
Costs and expenses:
Cost of sales (exclusive of items shown separately below)			716,645,000	592,530,000
Cost of other revenues (exclusive of items shown separately below)			10,172,000	28,422,000
Depreciation and depletion		47,413,000	97,209,000	75,413,000
Selling, general and administrative			36,626,000	36,453,000
Other postretirement benefits			0	0
Restructuring costs			0	0
Transaction and other costs			9,068,000	12,873,000
Total costs and expenses			869,720,000	745,691,000
Operating income (loss)			508,287,000	423,401,000
Interest expense, net			(37,314,000)	(6,947,000)
Reorganization items, net			0	0
Income (loss) before income taxes			470,973,000	416,454,000
Income tax (benefit) expense			(225,814,000)	(38,592,000)
Net income (loss)		$ (49,673,000)	$ 696,787,000	$ 455,046,000
Basic and diluted net income (loss) per share:
Net income (loss) per share—basic (in dollars per share)		$ (0.94)	$ 13.19	$ 8.62
Net income (loss) per share—diluted (in dollars per share)		$ (0.94)	$ 13.17	$ 8.62
Weighted average number of shares outstanding—basic (in shares)		52,640	52,812	52,800
Weighted average number of shares outstanding— diluted (in shares)		52,640	52,918	52,806
Dividends per share (in dollars per share)		$ 0	$ 6.73	$ 14.92
Predecessor
Revenues:
Total revenues	$ 71,383,000	$ 297,634,000
Costs and expenses:
Cost of sales (exclusive of items shown separately below)	72,297,000	244,723,000
Cost of other revenues (exclusive of items shown separately below)	4,698,000	19,367,000
Depreciation and depletion	28,958,000	47,413,000
Selling, general and administrative	9,008,000	20,507,000
Other postretirement benefits	6,160,000	0
Restructuring costs	3,418,000	0
Transaction and other costs	0	13,568,000
Total costs and expenses	124,539,000	345,578,000
Operating income (loss)	(53,156,000)	(47,944,000)
Interest expense, net	(16,562,000)	(1,711,000)
Reorganization items, net	7,920,000	0
Income (loss) before income taxes	(61,798,000)	(49,655,000)
Income tax (benefit) expense	18,000	18,000
Net income (loss)	(61,816,000)	(49,673,000)
Sales
Revenues:
Total revenues			$ 1,342,683,000	$ 1,124,645,000
Sales | Predecessor
Revenues:
Total revenues	65,154,000	276,560,000
Other revenues
Revenues:
Total revenues			$ 35,324,000	$ 44,447,000
Other revenues | Predecessor
Revenues:
Total revenues	$ 6,229,000	$ 21,074,000

STATEMENT OF CHANGES IN EQUITY

STATEMENT OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Common Stock	Preferred Stock	Treasury Stock [Member]	Additional Paid in Capital	Retained Earnings (Accumulated deficit)	Class A member units	Class A member unitsCommon Stock	Class A member unitsAdditional Paid in Capital	Class B member units	Class B member unitsCommon Stock	Class B member unitsAdditional Paid in Capital
Total net parent investment, beginning balance (Predecessor) at Dec. 31, 2015	$ (820,861)
Parent Net Investment Roll Forward [Roll Forward]
Net income (loss) | Predecessor	(61,816)
Change in attribution of Parent debt | Predecessor	(626)
Net transfers to Parent | Predecessor	(12,900)
Total net parent investment, ending balance (Predecessor) at Mar. 31, 2016	(896,203)
Parent Net Investment Roll Forward [Roll Forward]
Net income (loss) | Predecessor	(61,816)
Balance at end of period at Mar. 31, 2016	0	$ 0	$ 0	$ 0	$ 0	$ 0
Parent Net Investment Roll Forward [Roll Forward]
Net income (loss) | Predecessor	(49,673)
Net income (loss)	(49,673)					(49,673)
Net income (loss) | Predecessor	(49,673)
Net income (loss)	(49,673)					(49,673)
Other	509	7			502
Issuance of common shares, formerly member units							$ 601,783	$ 178	$ 601,605	$ 200,348	$ 348	$ 200,000
Balance at end of period at Dec. 31, 2016	752,967	533	0	0	802,107	(49,673)
Parent Net Investment Roll Forward [Roll Forward]
Net income (loss)	455,046					455,046
Net income (loss)	455,046					455,046
Other	4,181				4,181
Purchase accounting measurement period adjustment	(3,525)				(3,525)
Equity award modification	1,255				1,255
Dividends paid ($6.73 per share)	(796,902)				(474,025)	(322,877)
Common shares issued	1	1
Balance at end of period at Dec. 31, 2017	413,023	534	0	0	329,993	82,496
Parent Net Investment Roll Forward [Roll Forward]
Net income (loss)	696,787					696,787
Net income (loss)	696,787					696,787
Other	6,405				6,405
Dividends paid ($6.73 per share)	(360,635)				(91,122)	(269,513)
Common shares issued	0
Treasury stock purchase	(38,030)			(38,030)
Other	(4,938)	(1)			(5,449)	512
Balance at end of period at Dec. 31, 2018	$ 712,612	$ 533	$ 0	$ (38,030)	$ 239,827	$ 510,282

STATEMENT OF CHANGES IN EQUITY

STATEMENT OF CHANGES IN EQUITY (Parenthetical)	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Dividends per share (in dollars per share) | $ / shares	$ 14.92
Class A member units
Common stock shares issued (in shares)	17,772,724
Class B member units
Common stock shares issued (in shares)	34,864,802

STATEMENTS OF CASH FLOWS

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
OPERATING ACTIVITIES
Net income (loss)		$ (49,673)	$ 696,787	$ 455,046
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and depletion		47,413	97,209	75,413
Deferred income tax (benefit) expense		544	(223,038)	(1,686)
Stock-based compensation expense		509	6,405	4,181
Non-cash reorganization items		0	0	0
Amortization of debt issuance costs and debt discount, net		1,244	2,486	1,889
Accretion and valuation adjustment of ARO		2,817	(19,942)	1,834
Changes in operating assets and liabilities:
Trade accounts receivable		(54,911)	(20,653)	(51,850)
Other receivables		(2,530)	3,872	(8,121)
Income tax receivable		0	(12,431)	0
Inventories		9,524	(1,812)	(13,732)
Prepaid expenses and other current assets		(11,001)	1,444	(17,366)
Accounts payable		(4,144)	5,060	14,388
Accrued expenses and other current liabilities		45,408	13,835	15,642
Non-current income tax receivable		0	17,945	(39,255)
Other		5,613	(7,771)	(1,871)
Net cash provided by (used in) operating activities		(9,187)	559,396	434,512
INVESTING ACTIVITIES
Purchase of property, plant and equipment		(11,531)	(101,620)	(92,625)
Deferred mine development costs	$ 0	0	(8,937)	0
Proceeds from sale of property, plant and equipment		34	2,928	0
Cash paid for acquisition, net of cash acquired		(24,107)	0	0
Cash receipt from escrow agreement		9,364	0	0
Proceeds from termination of life insurance policy		12,857	0	0
Purchases of short-term investments		(17,501)	0	0
Net cash used in investing activities		(30,884)	(107,629)	(92,625)
FINANCING ACTIVITIES
Dividends paid		0	(360,635)	(796,902)
Proceeds from issuance of debt		0	128,750	344,750
Proceeds from rights offering		200,000	0	0
Retirements of debt		(2,295)	(3,060)	(3,060)
Principal repayments of capital lease obligations		0	0	(505)
Net cash transfers to Parent		0	0	0
Debt issuance costs paid		(4,978)	(3,713)	(2,562)
Common shares repurchased	0	0	(38,030)	0
Other	0	0	(4,938)	0
Net cash provided by (used in) financing activities		192,727	(281,626)	(458,279)
Net increase (decrease) in cash and cash equivalents and restricted cash		152,656	170,141	(116,392)
Cash and cash equivalents and restricted cash at beginning of period		0	36,264	152,656
Cash and cash equivalents and restricted cash at end of period	0	152,656	206,405	36,264
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Interest paid, net of capitalized interest		231	30,237	211
Cash paid for income taxes		0	3	2,349
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Capital leases - equipment			6,822	7,355
Assets acquired in Asset Acquisition (Note 3)			0	0
Liabilities assumed in Asset Acquisition (Note 3)			$ 0	$ 0
Predecessor
OPERATING ACTIVITIES
Net income (loss)	(61,816)	(49,673)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and depletion	28,958	47,413
Deferred income tax (benefit) expense	18	544
Stock-based compensation expense	390
Non-cash reorganization items	(18,882)
Amortization of debt issuance costs and debt discount, net	10,164
Accretion and valuation adjustment of ARO	1,169
Changes in operating assets and liabilities:
Trade accounts receivable	15,097
Other receivables	1,070
Income tax receivable	0
Inventories	677
Prepaid expenses and other current assets	13,020
Accounts payable	(15,338)
Accrued expenses and other current liabilities	(16,083)
Non-current income tax receivable	0
Other	858
Net cash provided by (used in) operating activities	(40,698)
INVESTING ACTIVITIES
Purchase of property, plant and equipment	(5,422)
Proceeds from sale of property, plant and equipment	0
Cash paid for acquisition, net of cash acquired	0
Cash receipt from escrow agreement	0
Proceeds from termination of life insurance policy	0
Purchases of short-term investments	0
Net cash used in investing activities	(5,422)
FINANCING ACTIVITIES
Dividends paid	0
Proceeds from issuance of debt	15,723
Proceeds from rights offering	0
Retirements of debt	(285)
Principal repayments of capital lease obligations	0
Net cash transfers to Parent	(13,290)
Debt issuance costs paid	(8,388)
Net cash provided by (used in) financing activities	(6,240)
Net increase (decrease) in cash and cash equivalents and restricted cash	(52,360)
Cash and cash equivalents and restricted cash at beginning of period	84,462	$ 32,102
Cash and cash equivalents and restricted cash at end of period	32,102
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Interest paid, net of capitalized interest	0
Cash paid for income taxes	0
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Capital leases - equipment	0
Assets acquired in Asset Acquisition (Note 3)	0
Liabilities assumed in Asset Acquisition (Note 3)	$ 0

Business and Basis of Presentat

Business and Basis of Presentation	12 Months Ended
	Dec. 31, 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” or, for the periods beginning as of April 1, 2016, the “Successor”) was formed on September 3, 2015 by certain Walter Energy, Inc. (“Walter Energy” or the “Parent”) lenders under the 2011 Credit Agreement, dated as of April 1, 2011 (the “2011 Credit Agreement”) and the noteholders under the 9.50% Senior Secured Notes due 2019 (such lenders and noteholders, collectively, “Walter Energy’s First Lien Lenders”) in connection with the acquisition by the Company of certain core operating assets of Walter Energy under section 363 under Chapter 11 of Title 11 (the "Chapter 11 Cases") of the U.S. Bankruptcy Code (“U.S. Bankruptcy Code”) in the Northern District of Alabama, Southern Division (the "Bankruptcy Court"). These operating assets acquired and liabilities assumed are referred to as the “Predecessor” for all periods on or before March 31, 2016. The Company and its Predecessor are 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 and South America. 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. On November 5, 2015, Walter Energy and certain of its wholly owned U.S. subsidiaries (collectively, the "Walter Energy Debtors") entered into an asset purchase agreement (as amended, the “Asset Purchase Agreement”) with the Company, pursuant to which, among other things, the Company, on behalf of Walter Energy’s First Lien Lenders, agreed to acquire the Predecessor through a credit bid of $ 1.1 billion and a release of the liens under the 2011 Credit Agreement and the 9.50% Senior Secured Notes due 2019 (“Walter Energy First Lien Obligations”), to assume certain liabilities of the Walter Energy Debtors and to pay cash consideration in accordance with sections 363 and 365 of the U.S. Bankruptcy Code (the “Asset Acquisition”). On January 8, 2016, the Bankruptcy Court approved the Asset Acquisition, which closed on March 31, 2016. In connection with the Asset Acquisition, the Company also conducted rights offerings to Walter Energy’s First Lien Lenders and certain qualified unsecured creditors to purchase newly issued Class B Units of the Company, which diluted the Class A Units on a pro rata basis (the “Rights Offerings”). Proceeds from the Rights Offerings were used to pay certain costs associated with the Asset Acquisition and for general working capital purposes. 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 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. Basis of Presentation Prior to the closing of the Asset Acquisition on March 31, 2016, the Company had no operations and nominal assets. The accompanying financial statements have been presented on a consolidated basis for the “Successor” periods subsequent to the Asset Acquisition, which include the year ended December 31, 2018 , the year ended December 31, 2017 , and the nine months ended December 31, 2016, and on a combined basis for the “Predecessor” periods prior to the Asset Acquisition, which includes the three months ended March 31, 2016. The financial information of the Company has been separated by a vertical line on the face of the financial statements to identify these different bases of accounting for Predecessor and Successor periods. Predecessor Presentation The Predecessor’s combined financial statements for the three months ended March 31, 2016 have been “carved-out” from the accounting records of Walter Energy. Historically, the Predecessor did not operate as an independent standalone company. For periods subsequent to filing the Chapter 11 Cases and prior to March 31, 2016, the Predecessor applied the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 852, Reorganizations, in preparing its combined financial statements. ASC 852 requires that the financial statements distinguish transactions and events that are directly associated with the reorganization from the ongoing operations of the business. Accordingly, certain revenues, expenses, realized gains and losses and provisions for losses that were realized or incurred in the Chapter 11 Cases have been recorded in a reorganization line item on the Combined Statements of Operations. Preparation of the combined financial statements, included making certain adjustments necessary to reflect all costs of doing business to present the historical records on a basis as if the Predecessor had been a separate standalone entity. These adjustments include, for example, allocations of Parent overhead and selling, general and administrative expenses. The historical costs and expenses reflected in the combined financial statements include an allocation for certain corporate functions historically provided by the Parent. Substantially all of the Predecessor’s senior management were employed by the Parent and certain functions critical to the Predecessor’s operations were centralized and managed by the Parent. Historically, the centralized functions included executive senior management, financial reporting, financial planning and analysis, accounting, shared services, information technology, tax, risk management, treasury, legal, human resources, and strategy and development. The costs of each of these services have been allocated to the Predecessor on the basis of the Predecessor’s relative headcount, revenue and total assets to that of the Parent. These cost allocations were $ 7.8 million for the three months ended March 31, 2016 (Predecessor). All intracompany transactions have been eliminated. The net effect of the settlement of transactions between the Predecessor, the Parent and other affiliates of the Parent, together with cash transfers to and from the Parent’s cash management accounts are reflected in the Statements of Changes in Stockholders' Equity and Parent Net Investment as net transfers to Parent and in the Statements of Cash Flows as a financing activity. The allocation methodologies have been described in these notes to the financial statements where appropriate, and management considers the allocations to be reasonable. The financial information included herein may not necessarily reflect the financial position, results of operations and cash flows of the Predecessor in the future or what they would have been had the Predecessor been a separate, standalone entity during the periods presented. The Parent used a centralized approach to cash management and financing of its operations. Historically, the majority of the Predecessor’s cash was transferred to the Parent on a daily basis. This arrangement is not reflective of the manner in which the Predecessor would have been able to finance its operations had it been a standalone business separate from the Parent during the periods presented. The Predecessor’s employees participated in benefit and stock-based compensation plans of the Parent. A portion of the cost of those plans is included in the combined financial statements. See Notes 14 and 15 for a further description of the accounting for benefit plans and stock-based compensation, respectively. The financial statements prior to April 1, 2016 included an allocation of a portion of debt and related interest expense from the Parent. Interest expense on the Parent’s debt attributed to the Predecessor was $16.6 million for the three months ended March 31, 2016 (Predecessor).

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Use of Estimates The Company prepares its financial statements in conformity with GAAP, which requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the periods presented. Due to the inherent uncertainty involved in making estimates, actual results could differ from those estimates. Concentrations of Credit Risk and Major Customers The Company’s principal line of business is mining and marketing met coal to foreign steel producers. For the year ended December 31, 2018 , approximately 97.4% of sales were derived from coal shipments to customers, located primarily in Europe, South America and Asia. At December 31, 2018 approximately 95.6% of trade receivables related to these customers. For the year ended December 31, 2018 , our geographic customer mix was 55% in Europe, 31% in South America and 14% in 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. During the year ended December 31, 2018 Xcoal Energy & Resources, Exiros BV Sucursal Uruguay and Huettenwerke Krupp Mannesmann GmbH accounted for $203.6 million , or 15.1% , $148.5 million , or 11.0% , and $141.3 million , or 10.5% of total revenues, respectively. During the year ended December 31, 2017 , Xcoal Energy & Resources and Salzgitter Flachstahl GmBH accounted for $181.9 million , or 16.1% , and $112.8 million , or 10% , of total revenues, respectively. During the nine months ended December 31, 2016, Salzgitter Flachstahl GmBH, Voestelpine and Huettenwerke Krupp Mannesmann GmBH accounted for $43.1 million , or 15.6% , $35.3 million , or 12.7% , and $34.0 million , or 12.3% of total revenues, respectively. During the three months ended March 31, 2016, Xcoal Energy & Resources and Voestelpine accounted for $10.7 million , or 16.4% and $8.3 million, or 12.8% of total revenues, respectively. Credit is extended based on an evaluation of the individual customer’s financial condition. In some instances, the Company requires letters of credit, cash collateral or prepayments from its customers on or before shipment to mitigate the risk of loss. These efforts have consistently resulted in minimal historical credit losses. 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 applied the standard to all customer contracts entered into as of the date of initial application. The Company concluded that the adoption did not change the timing at which the Company historically recognized revenue nor did it have a material impact on its consolidated financial statements. For periods prior to January 1, 2018, revenue was recognized when the following criteria had been met: (i) persuasive evidence of an arrangement existed; (ii) the price to the buyer was fixed or determinable; (iii) delivery had occurred; and (iv) collectability was 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 23. Our coal and gas sales generally include up to 45-day payment terms following the transfer of control of the goods to the customer. We typically do not include extended payment terms in our contracts with customers. Shipping and Handling Costs incurred to transport coal to the point of sale at the Port of Mobile, Alabama, are included in cost of sales and the gross amounts billed to customers, if any, to cover shipping and handling to the ultimate/final destination are included in sales. Cash and Cash Equivalents and Restricted Cash The following table provides a reconciliation of cash and cash equivalents and restricted cash reported within the Balance Sheets that sum to the total of the same such amounts shown in the Statements of Cash Flows (in thousands): Successor December 31, 2018 December 31, 2017 Cash and cash equivalents $ 205,577 $ 35,470 Restricted cash included in other long-term assets 828 794 Total cash and cash equivalents and restricted cash included in the Statements of Cash Flows $ 206,405 $ 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 December 31, 2018 and December 31, 2017 , restricted cash included in other long-term assets in the Balance Sheet represents amounts invested in certificate of deposits as financial assurance for post mining reclamation obligations. 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 December 31, 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. Inventories Inventories are valued at the lower of cost or net realizable value. Coal inventory costs include labor, supplies, equipment costs, operating overhead, freight, royalties, depreciation and depletion and other related costs. Coal inventories are valued using the first-in, first-out (“FIFO”) inventory valuation method. The valuation of coal inventories is subject to estimates due to possible gains and losses resulting from inventory movements from the mine site to storage facilities, inherent inaccuracies in belt scales and aerial surveys used to measure quantities and fluctuations in moisture content. Periodic adjustments to coal tonnages on hand are made for an estimate of coal shortages and overages due to these inherent gains and losses, primarily based on historical results from aerial surveys and periodic coal pile clean-ups. Supplies inventories are valued using the average cost method of accounting. Management evaluates its supplies inventory in terms of excess and obsolete exposures which includes such factors as anticipated usage, inventory turnover, inventory levels and ultimate market value. A reserve for excess and obsolete supplies inventory is established and charged to cost of sales in the Statements of Operations. Deferred Longwall Move Expenses Direct costs, including labor and supplies, associated with moving longwall equipment and the related equipment refurbishment costs are deferred and included in prepaid expenses. These deferred costs are amortized on a unit-of-production basis into cost of sales over the life of the subsequent panel of coal mined by the longwall equipment. See Note 5 for further disclosures related to deferred longwall move expenses. Advanced Mining Royalties Lease rights to coal reserves are often acquired in exchange for royalty payments. Advance mining royalties are advance payments made to lessors under terms of mineral lease agreements that are recoupable against future production royalties. These advance payments are deferred and charged to operations as the coal reserves are mined. Advance mining royalties are included in other long-term assets. Property, Plant and Equipment Property, Plant and Equipment Property, plant and equipment are recorded at cost. Depreciation is recorded principally on the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized on the straight-line method over the lesser of the useful life of the improvement or the remaining lease term. Estimated useful lives used in computing depreciation expense range from three to ten years for machinery and equipment, and from fifteen to thirty years for land improvements and buildings. Well life is used to estimate the useful life for gas properties and related development, and mine life is used for amortizing mine development costs. Gains and losses upon disposition are reflected in the Statements of Operations in the period of disposition. Maintenance and repair expenditures are charged to cost of sales as incurred. Deferred Mine Development Costs of developing new underground mines and certain underground expansion projects are capitalized. Underground development costs, which are costs incurred to make the coal physically accessible, may include construction permits and licenses, mine design, construction of access roads, main entries, airshafts, roof protection and other facilities. Mine development costs are amortized primarily on a unit-of-production basis over the estimated reserve tons directly benefiting from the capital expenditures. Costs amortized during the production phase of a mine are capitalized into inventory and expensed to cost of sales as the coal is sold. Owned and Leased Mineral Interests Costs to obtain coal reserves and lease mineral rights are capitalized based on cost or the fair value at acquisition and depleted using the unit-of-production method over the life of proven and probable reserves. Lease agreements are generally long-term in nature (original terms range from 10 to 50 years) and substantially all of the leases contain provisions that allow for automatic extension of the lease term provided certain requirements are met. Depletion expense was $9.6 million , $ 9.4 million , and $4.5 million for the years ended December 31, 2018 and December 31, 2017 , and the nine months ended December 31, 2016 , respectively, and is included in depreciation and depletion in the accompanying Statements of Operations. There was no depletion expense recorded for the three months ended March 31, 2016 (Predecessor). Asset Retirement Obligations The Company has certain asset retirement obligations primarily related to mine closing reclamation costs, perpetual water care costs and other costs associated with dismantling and removing facilities. Asset retirement obligations are determined for each mine using various estimates and assumptions, including estimates of disturbed acreage as determined from engineering data, estimates of future costs to reclaim the disturbed acreage and the timing of related cash flows, discounted using a credit-adjusted, risk-free rate. The Company's asset retirement obligations also include estimates to reclaim gas well in accordance with the Oil and Gas Board of Alabama. On at least an annual basis, the Company reviews the entire asset retirement obligation liability and makes necessary adjustments for permit changes, the anticipated timing of mine closures, and revisions to cost estimates and productivity assumptions to reflect current experience. As changes in estimates occur, the carrying amount of the obligation and asset are revised to reflect the new estimate after applying the appropriate credit-adjusted, risk-free discount rate. The future costs of these obligations are accrued at the estimated fair value in the period in which it is incurred if a reasonable estimate of fair value can be made. The present value of the estimated asset retirement cost is capitalized as part of the carrying amount of the long-lived asset. For sites where there is no asset, expense or income is recognized for changes in estimates. Capitalized asset retirement costs are amortized on a unit-of-production basis over the estimated reserves. Accretion of the asset retirement obligation is recognized over time and generally will escalate over the life of the producing asset, typically as production declines. Accretion is included in cost of sales on the Statements of Operations. Accrued mine closing costs, perpetual care costs and reclamation costs and other costs of dismantling and removing facilities are regularly reviewed by management and revised for changes in future estimated costs and regulatory requirements, as necessary. For ongoing operations, adjustments to the liability result in an adjustment to the corresponding asset. For some operations, adjustments to the liability are recognized as income or expense in the period the adjustment is recorded as no asset was recorded to offset the liability established during purchase accounting as the operations were idle at that time. Any difference between the recorded obligation and the actual cost of reclamation is recorded in profit or loss in the period the obligation is settled. See Note 9 for further disclosures related to asset retirement obligations. Impairment of Long-Lived Assets Property, plant and equipment and other long-lived assets are reviewed for impairment at least annually or whenever events or changes in circumstances indicate that the book value of the asset may not be recoverable. The Company periodically evaluates whether events and circumstances have occurred that would indicate possible impairment. When impairment indicators exist, the Company uses an estimate of the future undiscounted cash flows of the related asset or asset group over the remaining life in measuring whether or not the asset values are recoverable. If the carrying amount of an asset or asset group exceeds its estimated future cash flows, impairment is recognized equal to the amount by which the carrying amount of the asset exceeds the fair value of the asset or asset group. Fair value is generally determined using market quotes, if available, or a discounted cash flow approach. The Company’s estimate of future undiscounted cash flows is based on assumptions including long-term met coal pricing forecasts, anticipated production volumes and mine operating costs for the life of the mine or estimated useful life of the asset. Equity Award Compensation (Successor) The Company accounts for equity award-based compensation to employees and non-employee/directors in accordance with ASC 718 requiring employee equity awards to be accounted for under the fair value method adjusted for estimated forfeitures rates based on historical experience. The Company recognizes compensation expense associated with equity awards for all awards made to employees as the requisite service, performance and market vesting conditions are met. The Company measures compensation expense based on the grant-date fair value of the awards calculated using a Black-Scholes or Monte Carlo valuation model. Compensation expense for equity awards with a service-only condition is recognized over the employee’s requisite service period using a graded vesting method. For awards with a performance condition that affects vesting, the performance condition is not considered in determining the award’s grant-date fair value; however, the performance conditions are considered when estimating the quantity of awards that are expected to vest. No compensation expense is recorded for awards with performance conditions until the performance condition is determined to be probable of achievement. For awards with a market condition that affects vesting, the market condition is considered in determining the award’s grant-date fair value. Compensation expense for awards with a market condition is recognized straight-line over the derived or implied service period. For awards with both performance and market conditions, the market condition is incorporated into the fair value of the award, while the performance condition impacts the timing of expense recognition. Compensation expense for equity awards is included in cost of sales (exclusive of items shown separately below) and selling, general and administrative in the accompanying Statements of Operations. Stock-Based Compensation (Predecessor) Prior to the Asset Acquisition, the Parent periodically granted stock-based awards to its employees and its board of directors. Stock-based compensation expenses related to these awards were allocated to the Predecessor based on the awards and terms previously granted to the employees of the Predecessor’s business units or subsidiaries as well as an allocation of the Parent’s corporate employee expenses. The Parent measured stock options and other stock-based awards granted to employees and directors based on the fair value on the date of the grant and recognized compensation expense for those awards, net of estimated forfeitures, over the requisite service period, which was generally the vesting period of the respective award. The Parent recognized compensation expense for only the portion of awards that were expected to vest. In developing a forfeiture rate estimate, the Parent considered its historical experience to estimate pre-vesting forfeitures for service-based awards. The impact of a forfeiture rate adjustment was recognized in full in the period of adjustment, and when the actual forfeiture rate was materially different from the estimate. The Parent used the Black-Scholes option pricing model to value stock option grants and also estimated forfeitures in calculating the expense related to stock-based compensation. The Parent used the Monte Carlo simulation to value its performance share units in calculating the expense related to stock-based compensation. Deferred Financing Costs The costs to obtain new debt financing or amend existing financing agreements are deferred and amortized to interest expense over the life of the related indebtedness or credit facility using the straight line method. As of December 31, 2018 and December 31, 2017 , respectively, there were $ 3.1 million and $ 2.2 million , respectively, of origination fees related to the ABL Facility (as defined below) in other long-term assets on the accompanying Balance Sheet. As of December 31, 2018 and December 31, 2017 there were $6.8 million and $ 7.8 million , respectively of unamortized deferred financing costs and debt discount, net, related to the Notes (as defined below), which is presented as a net deduction from the carrying amount of the debt recognized in the accompanying Balance Sheet. Income Taxes The Company records a tax provision for the expected tax effects of the reported results of operations. The provision for income taxes is determined using the asset and liability method, under which deferred tax assets and liabilities are recognized for the expected future tax impact of temporary differences between the financial reporting and tax bases of assets and liabilities, and for operating losses and tax credit carryforwards. Deferred income tax assets and liabilities are measured using the currently enacted tax rates that apply to taxable income in effect for the years in which those tax assets and liabilities are expected to be realized or settled. The Company records a valuation allowance to reduce deferred income tax assets to the amount that is believed more likely than not to be realized. When the Company concludes that all or part of the net deferred income tax assets are not realizable in the future, the Company makes an adjustment to the valuation allowance that is charged to earnings in the period that such determination was made. The Company recognizes tax benefits from uncertain tax positions only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities, based on the technical merits of the position. The tax benefits recognized in the financial statements from such positions are then measured based on the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement. Results of operations of the Predecessor were historically included in the consolidated federal and state income tax returns of the Parent. The income tax provision included in the Predecessor financial statements was calculated using a method consistent with a separate return basis, as if the Predecessor’s business had been a separate taxpayer. Similarly, historical tax attributes (net operating losses, alternative minimum tax credits, etc.) were allocated to the Predecessor’s business utilizing a reasonable method of allocation. Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. A three level hierarchy has been established for valuing assets and liabilities based on how transparent (observable) the inputs are that are used to determine fair value, with the inputs considered most observable categorized as Level 1 and those that are the least observable categorized as Level 3. Hierarchy levels are defined as follows: Level 1: Quoted prices in active markets for identical assets and liabilities. Level 2: Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. Level 3: Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. New Accounting Pronouncements In February 2016, the FASB issued Accounting Standards Update ("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 adopted this standard on January 1, 2019 using the modified retrospective approach. The Company has concluded that the adoption of this standard did not have a material impact on the Company's consolidated financial position and results of operations. In August 2017, the FASB issued ASU 2017-12, “Targeted Improvements to Accounting for Hedging Activities.” The new guidance provides targeted improvements to the accounting for hedging activities to better align an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedging results. ASU 2017-12 is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years; early adoption is permitted. The Company is currently in the process of evaluating the standard.

Acquisition of the Predecessor

Acquisition of the Predecessor	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Acquisition of the Predecessor	Acquisition of the Predecessor On November 5, 2015, the Walter Energy Debtors entered into the Asset Purchase Agreement with the Company, pursuant to which, among other things, the Company, on behalf of Walter Energy’s First Lien Lenders, agreed to acquire the Predecessor via a credit bid and release of the liens on the Walter Energy First Lien Obligations. On January 8, 2016, the Bankruptcy Court approved the Asset Acquisition, which closed on March 31, 2016. The cash consideration of $ 50.8 million included the funding of escrow accounts to be used to pay certain expenses on behalf of the Walter Energy Debtors, some of which required residual amounts contained in the escrow accounts to be refunded to the Company after a specified time period. The Company received refunds of approximately $9.4 million during the nine months ended December 31, 2016, which is presented in the investing section of the Statement of Cash Flows. The net cash paid for the Asset Acquisition was $ 24.1 million , which was $ 50.8 million of cash paid less cash and cash equivalents acquired of $ 26.7 million . The purchase consideration has been allocated to the assets acquired and liabilities assumed based upon their estimated fair values at the date of the Asset Acquisition. During the first quarter of 2017, the Company completed the valuation of the assets and liabilities with the assistance of an independent third party and recorded a measurement-period adjustment to the preliminary purchase price allocation. The measurement-period adjustment was due to updated estimates for the acquired mineral interests including estimates for future royalty income, production volumes and timing which resulted in a $3.5 million decrease in fair value allocated to mineral interests as compared to the December 31, 2016 preliminary fair value. This also resulted in a decrease to additional paid in capital. The measurement-period adjustment was recorded during the first quarter of 2017 and had no impact on reported earnings for the years ended December 31, 2018 and 2017, respectively. In determining the fair values of net assets acquired in the Asset Acquisition, the Company considered, among other factors, the analyses of the Predecessor’s historical financial performance and estimates of the future performance of the acquired business, as well as the highest and best use of the acquired assets. Working capital, excluding inventory, and non-current restricted cash were recorded at the Predecessor’s carrying value, which is representative of the fair value on the date of acquisition. Inventory was valued at its net realizable value. Mineral interest was recorded at fair value utilizing the income approach. The income approach utilized the Company’s operating projections as of the valuation date. Under the income approach, fair value was estimated based upon the present value of future cash flows. A number of significant assumptions and estimates were involved in forecasting the future cash flows including sales volumes and prices, costs to produce (including costs for labor, commodity supplies and contractors), transportation costs, capital spending, working capital changes and a risk adjusted, after-tax cost of capital (all of which generally constitute unobservable Level 3 inputs under the fair value hierarchy). Property, plant and equipment, and other assets were recorded at fair values based on the cost and market approaches. The cost approach utilized trending and direct costing techniques to develop replacement costs. The market approach is based on independent secondary market data (which generally constitute Level 2 inputs under the fair value hierarchy). Black lung obligations and asset retirement obligations were recorded at fair value using a combination of market data, operational data and discounted cash flows and were adjusted by a discount rate factor reflecting current market conditions at the time of acquisition. The following tables summarize the final purchase price allocation, including the applicable measurement-period adjustments made upon finalization during the first quarter of 2017 (in thousands): Final purchase price: Cash paid $ 50,830 Fair value of First Lien Obligations relinquished in exchange for net assets of the Predecessor 598,607 Total purchase price $ 649,437 Final fair values of assets acquired and liabilities assumed: Cash and cash equivalents $ 26,723 Trade and other receivables 14,358 Inventories 46,464 Prepaid expenses and other current assets 30,722 Mineral interests 144,224 Property, plant and equipment 533,441 Other long-term assets 28,865 Total assets 824,797 Accounts payable 10,470 Accrued expenses 12,843 Other current liabilities 24,044 Current debt 2,879 Long-term debt 5,758 Deferred income taxes 1,400 Other long-term liabilities 117,966 Total liabilities 175,360 Total fair value of net assets acquired $ 649,437 Supplemental Unaudited Pro Forma Financial Information The following unaudited pro forma results of operations give effect to the Asset Acquisition as if it had occurred on January 1, 2015. This unaudited pro forma financial information should not be relied upon as necessarily being indicative of the historical results that would have been obtained if the Asset Acquisition had actually occurred on that date, nor the results of operations in the future. The supplemental unaudited pro forma financial information was adjusted to (i) reflect the impact of certain fair value adjustments, including an adjustment to depreciation and depletion expense as a result of a change in the basis of property, plant and equipment and mineral interests, (ii) eliminate historical interest expense related to the notes, loans and other debt that was not assumed by the Company as part of the Asset Acquisition, (iii) eliminate a gain on reorganization items associated with the Chapter 11 Cases and (iv) eliminate the Predecessor's historical other postretirement benefit expense associated with the Predecessor's historical other postretirement benefit obligations for retiree medical and life insurance benefits, which were not assumed by the Company. Successor For the year ended December 31, 2016 (in thousands) As (1) Pro forma (2) Revenue $ 297,634 $ 369,017 Net loss $ (49,673 ) $ (67,476 ) (1) Reflects nine months of Successor period operations. (2) Includes nine months of Successor period operations and three months of Predecessor period operations on a pro forma basis.

Inventories, net

Inventories, net	12 Months Ended
	Dec. 31, 2018
Inventory Disclosure [Abstract]
Inventories, net	Inventories, net Inventories, net are summarized as follows (in thousands): Successor December 31, 2018 December 31, 2017 Coal $ 32,854 $ 32,422 Raw materials, parts, supplies and other, net 23,865 21,872 Total inventories, net $ 56,719 $ 54,294

Prepaid Expenses and Other

Prepaid Expenses and Other	12 Months Ended
	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid Expenses and Other	Prepaid Expenses and Other Prepaid expenses and other consisted of the following (in thousands): Successor December 31, 2018 December 31, 2017 Deferred longwall move expenses $ 20,053 $ 19,600 Prepaid insurance 4,670 4,955 Prepaid deposits 692 1,043 Gas hedge asset — 1,664 Other 2,517 2,114 Total prepaid expenses and other $ 27,932 $ 29,376

Mineral Interests and Property,

Mineral Interests and Property, Plant and Equipment, Net	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Mineral Interests and Property, Plant and Equipment, net	Mineral Interests and Property, Plant and Equipment, net Mineral interests totaled $ 144.2 million and $ 144.2 million and the related accumulated depletion totaled $ 23.8 million and $ 14.2 million as of December 31, 2018 and December 31, 2017 , respectively. Property, plant and equipment are summarized as follows (in thousands): Successor December 31, 2018 December 31, 2017 Land $ 72,139 $ 72,882 Land improvements 18,083 11,444 Building and leasehold improvements 71,561 82,836 Mine development and infrastructure costs 3,567 308 Machinery and equipment 512,594 441,353 Construction in progress 46,814 39,671 Total 724,758 648,494 Less: Accumulated depreciation (184,443 ) (111,749 ) Property, plant and equipment, net $ 540,315 $ 536,745 Depreciation and depletion expense was $ 97.2 million , $ 75.4 million , $47.4 million , and $29.0 million for the years ended December 31, 2018 and December 31, 2017 , the nine months ended December 31, 2016 and the three months ended March 31, 2016 (Predecessor), respectively.

Other Long-Term Assets

Other Long-Term Assets	12 Months Ended
	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Other Long-Term Assets	Other Long-Term Assets Other long-term assets consisted of the following (in thousands): Successor December 31, 2018 December 31, 2017 Advance mining royalties $ 10,910 $ 10,342 Restricted cash 828 794 Other 9,301 7,306 Total other long-term assets $ 21,039 $ 18,442

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Tax Cuts and Jobs Act was enacted on December 22, 2017. The Tax Cuts and Jobs Act significantly revised the U.S. corporate income tax regime by, among other things, lowering the U.S. corporate tax rate from 35% to 21% effective January 1, 2018, while also repealing the deduction for domestic production activities, implementing a territorial tax system, limiting the deduction for interest expense, limiting the use of net operating losses generated on or after January 1, 2018 to offset taxable income and repealing the corporate alternative minimum tax ("AMT") and triggering refunds of prior year AMT credits. On December 22, 2017, the SEC staff issued Staff Accounting Bulletin No. 118 ('SAB 118") to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Tax Cuts and Jobs Act. The Company applied SAB 118 to recognize the provisional tax impacts related to the revaluation of deferred tax assets and liabilities and the impact of AMT tax credits in its consolidated financial statements for the year ended December 31, 2017. On January 14, 2019, the Internal Revenue Service ("IRS") issued a statement that AMT refunds for taxable years beginning after December 31, 2017 will not be subject to sequestration which reversed an earlier IRS announcement that refundable AMT credits would be subject to sequestration. As a result, in the fourth quarter of 2018, the Company completed its accounting for the income tax effects of the Tax Cuts and Jobs Act and recorded a measurement period adjustment recognizing an income tax receivable and related income tax benefit of $2.8 million . As of December 31, 2018, the Company has a current income tax receivable of $21.6 million and a non-current income tax receivable of $21.3 million of AMT credits, which are expected to be received in 2019 through 2022. Income Tax Expense (Benefit) Income tax expense (benefit) consisted of the following (in thousands): Successor Predecessor For the year ended For the year ended For the nine months ended For the three 2018 2017 2016 2016 Current Federal $ (2,776 ) $ (36,906 ) $ (526 ) $ — State — — — — (2,776 ) (36,906 ) (526 ) — Deferred Federal (176,141 ) (1,712 ) 542 16 State (46,897 ) 26 2 2 (223,038 ) (1,686 ) 544 18 Total $ (225,814 ) $ (38,592 ) $ 18 $ 18 Total income tax expense (benefit) differs from the expected tax expense (benefit) (computed by multiplying the U.S. federal statutory rate of 21% in 2018 and 35% in both 2017 and 2016 by income before income taxes) as a result of the following (in thousands): Successor Predecessor For the year ended For the year ended For the nine months ended For the three 2018 2017 2016 2016 Income (loss) before income tax expense (benefit) $ 470,973 $ 416,454 $ (49,655 ) $ (61,798 ) Tax expense (benefit) at statutory tax rate 98,904 145,759 (17,379 ) (21,629 ) Effect of: Depletion (18,227 ) (25,212 ) — — Estimate of the Tax Cuts and Jobs Act impact (2,775 ) (38,592 ) — — State and local income tax, net of federal effect 14,897 9,620 (1,051 ) (1,615 ) Valuation allowance on deferred tax assets (312,493 ) (129,245 ) 14,460 22,204 Non-deductible transaction costs 566 4,506 4,318 — Impact of restructuring — — — 1,111 Other (6,686 ) (5,428 ) (330 ) (53 ) Tax expense (benefit) recognized $ (225,814 ) $ (38,592 ) $ 18 $ 18 Deferred Taxes Deferred income tax assets and liabilities reflect the effects of tax losses, credits, and the future income tax effects of temporary differences between the financial statement carrying amounts of assets and liabilities and their respective tax bases. Deferred income tax assets and liabilities are measured using enacted tax rates that apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. Significant components of the Company's deferred income tax assets and liabilities were (in thousands): Successor December 31, 2018 December 31, 2017 Deferred income tax assets: Net operating loss and credit carryforwards $ 298,180 $ 395,526 Inventory 119 1,083 Asset retirement obligations 15,526 23,765 Black lung obligations 6,720 7,991 Accrued expenses 3,611 561 Other 2,767 197 Total 326,923 429,123 Less: valuation allowance for deferred income tax assets — (312,493 ) Net deferred income tax assets 326,923 116,630 Deferred income tax liabilities: Prepaid expenses (9,894 ) (9,416 ) Property, plant and equipment (92,361 ) (105,715 ) Other (1,888 ) (1,757 ) Total deferred income tax liabilities (104,143 ) (116,888 ) Net deferred income tax asset (liability) $ 222,780 $ (258 ) On March 31, 2016, the Company experienced an ownership change for purposes of Section 382 of the Internal Revenue Code of 1986, as amended (the "Code"). As a result of such ownership change, absent an applicable exception to such rules, an annual limitation under Section 382 would apply for federal and certain state income tax purposes with respect to the utilization of net operating loss carryforwards ("NOLs"). In 2017, the Company requested a private letter ruling ("PLR") from the Internal Revenue Service ("IRS") to clarify certain matters, that if ruled favorably on by the IRS, would allow the Company to qualify for an exception to the aforementioned rules limiting its utilization of its NOLs. On September 18, 2017, the IRS issued to the Company a favorable PLR. Prior to the issuance of the PLR, the Company operated and prepared its financial statements based on an assumption that an annual limitation on the utilization of the NOLs existed. As a result of qualifying for such exception, the Company's gross federal and state NOLs were revised downward to approximately $1.9 billion and $2.0 billion , respectively, as of December 31, 2016 and $1.6 billion for both federal and state NOLs as of December 31, 2017. This revision reflected a decrease to the NOL deferred tax asset and a corresponding adjustment to the valuation allowance recorded against those NOLs. If the Company were to undergo a subsequent ownership change our ability to utilize our NOLs and other tax attributes could be subject to severe limitations. The Company has federal net operating loss carryforwards of approximately $1.1 billion as of December 31, 2018, which expire predominantly in December 31, 2034 through December 31, 2036. The Company has state net operating loss carryforwards of approximately $1.2 billion , which expire predominantly in December 31, 2029 through December 31, 2031. In addition, the Company has approximately $11.5 million of general business credits which begin to expire in December 31, 2027 and fully expire in December 31, 2034. Valuation Allowance The Company periodically assesses whether it is more likely than not that it will generate sufficient taxable income to realize its deferred income tax assets. The Company establishes valuation allowances if it is not likely it will realize its deferred income tax assets. In making this determination, the Company considers all available positive and negative evidence and makes certain assumptions. The Company considers, among other things, all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, the overall business environment, its historical financial results, the industry's historically cyclical financial results, its cumulative three-year income or loss position and potential current and future tax planning strategies. The Company recorded a full valuation allowance in 2016 due to the Company being in a three-year cumulative loss position at that time, compounded by the negative industry-wide business trends and outlook. At December 31, 2017, the Company had a $312.5 million valuation allowance established against its deferred income tax assets, which represented a full valuation allowance against its net deferred income tax assets. For 2017, the Company recorded a pre-tax profit of $416.5 million ; however, the Company remained in a three-year cumulative loss position, had limited operating results as a new Company and given the industry's recent history of significant losses concluded as of December 31, 2017 that another year of significant profitability was needed to support a release of the valuation allowance. During 2018, the Company continued the trend of sustained profitability, recording a pre-tax profit of $471.0 million for the year. During the fourth quarter of 2018, after considering all relevant factors, the Company concluded that its deferred income tax assets are more likely than not to be realized. In evaluating the likelihood of utilizing its deferred tax assets, the significant relevant factors that the Company considered are: (1) its recent history of profitability; (2) growth in the U.S. and global economies; (3) estimates of future met coal prices; (4) the Company moved from a three-year cumulative loss position to a cumulative income position for the first time since it established the full valuation allowance; and (5) future impact of taxable temporary differences. Based on this evaluation, at December 31, 2018, the Company released its valuation allowance against its net deferred income tax assets resulting in a $225.8 million income tax benefit. The following table shows the balance of our valuation allowance and the associated activity: Successor December 31, 2018 December 31, 2017 Beginning balance $ 312,493 $ 767,290 Addition/(Reduction) - current tax expense/(benefit) (86,679 ) (129,245 ) Reduction due to application of IRC Section 382 — (130,327 ) Estimate of Tax Cuts and Jobs Act impact — (195,225 ) Release $ (225,814 ) $ — Ending balance $ — $ 312,493 Uncertain Tax Positions The Parent filed income tax returns in the U.S. and in various state and local jurisdictions which are routinely examined by tax authorities in these jurisdictions. Net operating losses and carryforwards are subject to adjustments based on examination and the statute of limitations is currently open for all such loss and credit carryforwards. The Company had no unrecognized tax benefits or accruals for unrecognized tax benefits as of December 31, 2018 and 2017, respectively. The Company did not record any interest or penalties associated with income taxes but would record interest and penalties within income tax expense.

Asset Retirement Obligation

Asset Retirement Obligation	12 Months Ended
	Dec. 31, 2018
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations	Asset Retirement Obligations Changes in the asset retirement obligations (“ARO”) were as follows (in thousands): Successor For the twelve months ended December 31, 2018 For the twelve months ended Balance at Beginning of Period $ 99,668 $ 99,148 ARO liability assumed in the Asset Acquisition — — Accretion expense 4,619 1,834 Revisions to estimates (42,064 ) (658 ) Obligations settled (399 ) (656 ) Balance at End of Period $ 61,824 $ 99,668 The portion of costs expected to be paid within a year of December 31, 2018 is $ 2.8 million . The portion of costs expected to be incurred beyond one year as of December 31, 2018 is $ 59.0 million . There were no assets that were legally restricted for purposes of settling asset retirement obligations at December 31, 2018 . Alabama's regulatory framework technically allows for self-bonding, as a practical matter, due to the onerous regulatory requirements for self-bonding, mining companies in Alabama utilize surety bonds, collateral bonds, or letters of credit to meet their financial assurance requirements. At December 31, 2018 , the Company had outstanding surety bonds and letters of credit with parties for post-mining reclamation at all of its mining operations totaling $44.4 million , and $2.1 million for miscellaneous purposes. Additionally, the Company had $0.8 million invested in certificate of deposits as financial assurance for post mining reclamation obligations. For the year ended December 31, 2018 and December 31, 2017 , the reduction to the liability was primarily attributable to the net impact of changes in discount rates, current estimates of the costs and scope of remaining reclamation work and fluctuations in projected mine life estimates. For the year ended December 31, 2018 , $24.6 million or $0.47 per share, of the adjustment to the liability was reflected as income in the period because there was no asset recorded to offset the adjustment to the liability. This portion of the liability relates to operations that were idle at the time of purchase accounting and no value was attributed to any asset as an offset for the asset retirement obligation.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued Expenses	Accrued Expenses Accrued expenses consisted of the following (in thousands): Successor December 31, 2018 December 31, 2017 Accrued wages and employee benefits $ 37,221 $ 24,832 Accrued operating expenses 20,383 17,203 Accrued royalties 8,617 9,185 Accrued freight 4,053 5,051 Accrued interest 6,333 4,589 Accrued non-income taxes 1,642 1,553 Other 4,093 4,291 Total accrued expenses $ 82,342 $ 66,704

Reorganization Items, Net

Reorganization Items, Net	12 Months Ended
	Dec. 31, 2018
Reorganizations [Abstract]
Reorganization Items, Net	Reorganization Items, Net Expenses and income directly associated with the Chapter 11 Cases are reported separately in the Statements of Operations as reorganization items as required by ASC 852. Reorganization items also include adjustments to reflect the carrying value of liabilities subject to compromise at their estimated allowed claim amounts, as such adjustments are determined. Reorganization items include an allocation of professional fees incurred in relation to the Chapter 11 Cases. For the three months ended March 31, 2016 (Predecessor), the cost of these professional fees was allocated on the basis of the Predecessor’s assets as compared to the total assets of the Parent. The following table presents reorganization items (in thousands): Predecessor For the three months ended 2016 Professional fees (10,962 ) Rejected executory contracts, leases and other 18,882 Reorganization items, net $ 7,920 Net cash paid for reorganization items for the three months ended March 31, 2016 (Predecessor) totaled approximately $ 12.3 million .

Restructuring Costs

Restructuring Costs	12 Months Ended
	Dec. 31, 2018
Restructuring and Related Activities [Abstract]
Restructuring Costs	Restructuring Costs For the three months ended March 31, 2016 (Predecessor), the Predecessor recognized restructuring charges of approximately $ 3.4 million , due to workforce reductions at the Alabama No. 7 underground mine, the Alabama No. 4 underground mine and corporate headquarters in conjunction with cost containment initiatives implemented in response to the deterioration in the metallurgical coal market. The restructuring charges consist primarily of severance and related benefits costs. The Company does not expect to incur any additional restructuring charges in the Successor periods in connection with the Predecessor restructuring actions.

Pneumoconiosis ("Black Lung") O

Pneumoconiosis ("Black Lung") Obligations Pneumoconiosis ("Black Lung") Obligations	12 Months Ended
	Dec. 31, 2018
Self Insurance Reserve Disclosure [Abstract]
Pneumoconiosis (Black Lung) Obligations	Pneumoconiosis ("Black Lung") Obligations The Company is responsible for medical and disability benefits for black lung disease under the Federal Coal Mine Health and Safety Act of 1969, as amended. Beginning on April 1, 2016 through May 31, 2018, the Company was insured under a guaranteed cost insurance policy, through a third-party insurance carrier, for black lung claims raised by any employee subsequent to the Asset Acquisition. Beginning June 1, 2018, the Company has a deductible policy where the Company is responsible for the first $0.5 million for each black lung claim. In addition, in connection with the Asset Acquisition, the Company assumed all black lung liabilities of Walter Energy and its U.S. subsidiaries incurred prior to March 31, 2016. The Company is self-insured for the black lung claims assumed in the Asset Acquisition. Due to a limited operating history as a stand-alone company and as a result of being self-insured for these historical black lung claims, the Department of Labor required the Company to post $ 17.5 million in Treasury bills as collateral, in addition to maintaining a black lung trust acquired in the Asset Acquisition. The $ 17.5 million of collateral is recognized as short-term investments and the $ 3.6 million and $ 4.0 million black lung trust is offset against the long-term portion of the black lung obligations within the Balance Sheet as of December 31, 2018 and December 31, 2017, respectively. Under the terms of the agreement with the U.S. Department of Labor, the Company may elect to replace the $ 17.5 million collateral deposit with a surety bond or other form of assurance every six months. The estimated total black lung liabilities (net of black lung trust assets) were $ 26.8 million as of December 31, 2018 , of which $ 1.6 million is classified in other current liabilities and the remainder of $ 25.2 million is shown as a long-term liability in a separate line item in the Consolidated Balance Sheet. For the year ended December 31, 2017 , the estimated black lung liabilities were $ 31.9 million , of which $ 1.7 million is classified in other current liabilities and $ 30.2 million is displayed as a long-term liability in a separate line item in the Balance Sheet. The Company performs an annual evaluation of its black lung liabilities at each balance sheet date. The calculation uses assumptions regarding rates of successful claims, discount factors, benefit increases and mortality rates, among others.

Pension and Other Postretiremen

Pension and Other Postretirement Benefits	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Pension and Other Postretirement Benefits	Pension and Other Postretirement Benefits Successor Benefit Plans In connection with the Asset Acquisition, the Company did not assume any of the Parent’s obligations under the plans discussed in further detail below. The Company established new employee benefit plans for its employees subsequent to closing the Asset Acquisition. The plans are defined contribution plans. Contributions to these defined contribution plans amounted to $ 3.1 million for the year ended December 31, 2018 , $ 1.4 million for the year ended December 31, 2017 and $1.1 million for the nine months ended December 31, 2016. New Initial CBA In connection with the Asset Acquisition, the Company negotiated a new initial collective bargaining agreement (“CBA”) with the United Mine Workers of America ("UMWA") (the “UMWA CBA”), which was ratified by UMWA’s members on February 16, 2016 and expires on March 31, 2021. Pursuant to the UMWA CBA, the Company agreed to contribute $25.0 million to a Voluntary Employee Beneficiary Association (“VEBA”) trust formed and administered by the UMWA. Approximately 69% of the Company's employees were represented by the UMWA as of December 31, 2018 and December 31, 2017 . Predecessor Benefit Plans In the Predecessor periods, the Parent had various defined benefit pension plans covering eligible salaried and hourly employees. The Parent also provided certain postretirement benefits other than pensions, primarily healthcare, to eligible retirees. In addition to its own pension plans and other postretirement benefit plans, the Parent contributed to several multi-employer benefit plans covering eligible employees who were represented by the UMWA. The Parent funded its defined benefit pension plans in amounts sufficient to satisfy the “Minimum Funding Standards” of the Employee Retirement Income Security Act of 1974 (“ERISA”). Other postretirement benefit plans were funded as benefits were paid or as assessed by third-party plan sponsors. On December 28, 2015 the Bankruptcy Court entered the Memorandum Opinion and Order Granting Debtors’ Motion for an Order (I) authorizing the Walter Energy Debtors to (A) reject collective bargaining agreements, (B) implement final labor proposals, and (C) terminate retiree benefits; and (II) granting related relief, authorizing the Walter Energy Debtors to reject their collective bargaining agreements with the UMWA (the “UMWA Order”). The UMWA Order authorized the Walter Energy Debtors to reject their collective bargaining agreements with the UMWA and allow for the sale of the Walter Energy Debtors’ assets free and clear of collective bargaining obligations. The contributions to the Parent’s defined benefit plans related to the Predecessor’s employees recognized as expenses were $6.2 million for the three months ended March 31, 2016 (Predecessor). UMWA Multi-employer Benefit Plans The Parent was required under its agreement with the UMWA to contribute to multiemployer plans providing pension, healthcare and other postretirement benefits. At December 31, 2015, approximately 61.4% of the Predecessor’s workforce was represented by the UMWA and covered under the Predecessor’s collective bargaining agreement, which began July 11, 2012 and was to expire December 31, 2016. The Predecessor’s obligations to make contributions to the UMWA multi-employer pension and benefit plans ceased upon entry of the UMWA Order by the Bankruptcy Court effective as of March 31, 2016. The Parent was required under its agreements with the UMWA, specifically the 1974 UMWA Pension Plan, the UMWA Combined Benefit Fund, the UMWA 1992 Benefit Fund, the UMWA 1993 Benefit Plan, and the 2012 Retiree Bonus Plan, to pay amounts based principally on hours worked by UMWA represented employees. Contributions under the UMWA multi-employer pension and benefit plans were set at an aggregate rate of $8.16 per hour worked. Aggregate contributions related to the Predecessor’s employees under these plans were approximately $6.2 million for the three months ended March 31, 2016 (Predecessor).

Equity Award Plans

Equity Award Plans	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity Award Plans	Equity Award Plans Warrior Met Coal, LLC 2016 Equity Incentive Plan The Company adopted the Warrior Met Coal, LLC 2016 Equity Incentive Plan (the “2016 Equity Plan”). Under the 2016 Equity Plan, employees, directors and officers of the Company were granted equity interests in Warrior Met Coal, LLC in the form of restricted units and phantom units. In connection with the corporate conversion on April 12, 2017, the awards of restricted units were converted into restricted shares of common stock of the Company (the "Restricted Shares"). The Restricted Shares have certain service-based, performance-based and market-based vesting conditions, including the occurrence of an initial public offering or a change in control as set forth in the 2016 Equity Plan and the applicable award agreements. As of December 31, 2018 , 805,083 Restricted Shares were issued, of which, approximately 25,335 had been forfeited and 630,209 had vested. Upon effectiveness of the 2017 Equity Plan (defined below), no further awards were granted under the 2016 Equity Plan. Holders of phantom shares have the right to receive shares of the Company on the earlier of (i) a change in control as defined by the 2016 Equity Plan or (ii) the fifth anniversary of the grant date of the phantom share. The phantom shares are settled in the Company’s shares. As of December 31, 2018 , there were 43,580 phantom shares issued to a director of the Company, all of which were fully vested upon issuance. Restricted Shares were issued proportionally as Tranche A, Tranche B, and Tranche C shares. The Tranche A shares have service and performance based vesting conditions and the awards vest in equal installments on each of the first five anniversaries of the grant date that occurs prior to an IPO and thereafter, subject to the employee’s continued employment or the director’s continued service with the Company through these dates. Vesting is conditioned and contingent upon at least 50% of the shares originally acquired by Walter Energy’s First Lien Lenders in the Asset Acquisition having been disposed of to an independent third party, whether before or after the IPO. 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 public secondary offerings (see Note 19). In connection with the first of these secondary offerings, the performance based vesting condition was met resulting in approximately $3.6 million of incremental stock compensation expense. The remaining awards shall vest over the remaining time based vesting conditions. As of December 31, 2018 , 98,126 Tranche A shares have vested. In the event of a change in control, any Tranche A shares that have not previously vested shall become fully vested at the time of such change in control, subject to the employee’s continued employment or the director's continued service with the Company through the change in control date. The Tranche B and Tranche C shares are performance and market- based awards, with vesting being contingent upon the achievement of certain market conditions and subject to the employee’s continued employment or the director's continued service with the Company through the date of achievement. In 2017, 532,083 Tranche B and Tranche C shares met the required performance and market conditions and were fully vested. In connection with the vesting of the Tranche B and C shares, the Company recognized approximately $3.2 million in stock compensation expense for the year ended December 31, 2017. The Company also recognized an excess income tax benefit of $3.4 million in connection with this vesting. As of December 31, 2018 , unrecognized compensation expense related to the 2016 Equity Plan amounted to approximately $1.0 million . The following table presents a summary of Restricted Shares granted under the 2016 Equity Plan for the year ended December 31, 2018 : Number of Restricted Class C Shares Weighted Average Grant Date Fair Value Non-vested at December 31, 2017 266,027 $ 21.34 Granted — Forfeited (18,362 ) $ 21.34 Vested (98,126 ) $ 21.34 Outstanding at December 31, 2018 149,539 $ 21.34 The Company used the Black-Scholes option pricing model to estimate the fair value of restricted Tranche A shares granted and the Monte Carlo pricing model to estimate the fair value of restricted Tranche B and C shares granted. The pricing model incorporated the assumptions as presented in the following table, shown at their weighted average values: Successor For the year ended December 31, 2017 For the nine months ended December 31, 2016 Expected stock price volatility (a) 35% 25.25% Risk-free interest rate (b) 1.75% 1.25% Expected life (years) (c) 4.17 5.00 (a) The Company bases its expected volatility on a group of companies believed to be a representative peer group, selected based on industry and market capitalization. (b) The risk-free rate for periods within the expected term of the award is based on the U.S. Government Bond yield with a term equal to the awards' expected term on the date of grant. (c) Expected life represents the period of time that awards granted are expected to be outstanding. Warrior Met Coal, Inc. 2017 Equity Incentive Plan In connection with the IPO, the Company adopted the Warrior Met Coal, Inc. 2017 Equity Incentive Plan (the “2017 Equity Plan”). Awards previously issued and outstanding under the 2016 Equity Plan will continue to be governed by the 2016 Equity Plan. However, no further awards will be granted under the 2016 Equity Plan. Under the 2017 Equity Plan, directors, officers, employees, consultants and advisors and those of affiliated companies, as well as those who have accepted offers of employment or consultancy from the Company or the Company’s affiliated companies, may be granted equity interest in Warrior Met Coal, Inc. in the form of stock options, stock appreciation rights, restricted stock, restricted stock units, stock bonus awards, and performance awards. The total number of shares of common stock, including incentive stock options, available for grant of awards under the 2017 Equity Plan as of December 31, 2018 is 5,657,450 . If any outstanding award expires, is canceled, forfeited, or settled in cash, the shares allocable to that award will again be available for grant under the 2017 Equity Plan. As of December 31, 2018 the equity awards granted under the 2017 Equity Plan are comprised of common stock, restricted stock awards, and restricted stock unit awards. The Company recognized stock compensation expense of $2.1 million for the year ended December 31, 2018 associated with the granting of the awards. Unrecognized compensation expense related to the 2017 Equity Plan amounted to approximately $1.5 million as of December 31, 2018 . A summary of activity related to restricted stock unit award grants under the 2017 Equity Incentive Plan during the year ended December 31, 2018 is as follows: Shares Weighted Average Grant Date Fair Value Non-vested at December 31, 2017 8,823 $ 18.51 Granted 201,512 $ 27.71 Forfeited (15,935 ) $ 27.92 Vested (2,875 ) $ 18.39 Outstanding at December 31, 2018 191,525 $ 27.30 Equity Modification On March 31, 2017, the board of managers of the Company 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 “Special Distribution”). The Special Distribution with respect to such Restricted Shares was not paid but held in trust pending their vesting. As of December 31, 2018 , approximately $5.4 million is held in the trust and is included within other long-term assets in the accompanying Balance Sheets. On June 1, 2017, the Compensation Committee (the "Committee") of the board of directors of the Company (the "Board") approved the modification described below (the “Modification”) to the award agreements (the “Awards”) for the Restricted Shares to certain officers, directors and employees of the Company. Pursuant to the Modification, the Committee waived certain vesting requirements with respect to the Special Distribution for the Restricted Shares such that funds currently held in trust as described above with respect to the Special Distribution were paid in full to recipients that received equal to or less than $100.0 thousand and were paid with respect to 50% of the Restricted Shares for recipients that received greater than $100.0 thousand . However, funds held in trust with respect to the Special Distribution for the remaining 50% of the Restricted Shares for recipients that received greater than $100.0 thousand will not be released until such shares vest pursuant to the original terms of the Awards on the basis of the passage of time and the Company’s achievement of certain metrics. In addition and pursuant to the Modification, the holders of the Restricted Shares were permitted to elect to receive the 2017 Dividend released from trust as described above with respect to their Restricted Shares (i) 100% in cash; (ii) 50% in cash and 50% in restricted stock units (“RSUs”); or (iii) 100% in RSUs. In connection with the Modification, the Committee approved a form of Restricted Stock Unit Award Agreement (the “RSU Award Agreement”) pursuant to the 2017 Equity Plan on June 1, 2017 (the “Grant Date”) for those holders who elected to receive the Special Distribution, in whole or in part, in RSUs (the “Participants”). The RSU Award Agreement provides that RSUs awarded pursuant to the Modification shall be fully vested on the Grant Date and shall be settled in shares of common stock on a one -for-one basis on the earliest of (i) one -third on each of the first three anniversaries of the Grant Date; (ii) a Change in Control (as defined in the 2017 Equity Plan); (iii) the Participant’s separation from service with the Company or its affiliates; or (iv) death of the Participant. In connection with the Modification, for the year ended December 31, 2017 , the Company recognized a reduction to dividends payable of $0.2 million associated with the holders that elected to receive cash and $1.3 million was treated as an adjustment to equity for those that elected RSUs. Predecessor Stock-Based Compensation Certain of the Predecessor’s employees participated in stock-based compensation plans sponsored by the Parent. For the three months ended March 31, 2016 (Predecessor) the Predecessor recorded stock-based compensation expense related to equity awards granted by the Parent totaling approximately $0.4 million .

Debt

Debt	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Debt	Debt Debt consisted of the following (in thousands): December 31, 2018 December 31, 2017 Weighted Average Interest Rate at December 31, 2018 Final Maturity Senior secured notes $ 475,000 $ 350,000 8% 2024 Promissory note 760 3,725 4% 2019 Debt discount, net (6,769 ) (7,812 ) Total debt 468,991 345,913 Less: current debt (760 ) (2,965 ) Total long-term debt $ 468,231 $ 342,948 The Company's minimum debt repayment schedule, excluding interest, as of December 31, 2018 is as follows (in thousands): Payments Due 2019 2020 2021 2022 2023 Thereafter Senior secured notes $ — $ — $ — $ — $ — $475,000 Promissory note 760 — — — — — Total $ 760 $ — $ — $ — $ — $ 475,000 ABL Facility On October 15, 2018, the Company entered into an Amended and Restated Asset-Based Revolving Credit Agreement, by and among the Company and certain of its subsidiaries, as borrowers, the guarantors party thereto, the lenders from time to time party thereto and Citibank, N.A, as administrative agent and collateral agent (in such capacities, the "Agent"), which amended and restated in its entirety the existing ABL Facility, and, among other things (i) increased the aggregate commitments available to be borrowed under the ABL Facility to $125.0 million , (ii) extended the maturity date of the ABL Facility to October 15, 2023, (iii) decreased the applicable interest rate margins with respect to the loans and the applicable fees in connection with the issuance of letters of credit, and (iv) amended certain covenants and other terms and provisions. Under the ABL Facility, up to $10.0 million of the commitments may be used to incur swingline loans from Citibank and up to $50.0 million of the commitments may be used to issue letters of credit. The ABL Facility will mature on October 15, 2023. As of December 31, 2018 , no loans were outstanding under the ABL Facility and there were $4.6 million of letters of credit issued and outstanding under the ABL Facility. At December 31, 2018 , the Company had $120.4 million of availability under the ABL Facility (calculated net of $4.6 million of letters of credit outstanding at such time). The ABL Facility contains customary covenants for asset-based credit agreements of this type, including among other things: (i) requirements to deliver financial statements, other reports and notices; (ii) restrictions on the existence or incurrence of certain indebtedness; (iii) restrictions on the existence or incurrence of certain liens; (iv) restrictions on making certain restricted payments; (v) restrictions on making certain investments; (vi) restrictions on certain mergers, consolidations and asset dispositions; (vii) restrictions on certain transactions with affiliates; and (viii) restrictions on modifications to certain indebtedness. Additionally, the ABL Facility contains a springing fixed charge coverage ratio of not less than 1.00 to 1.00, which ratio is tested if availability under the ABL Facility is less than a certain amount. As of December 31, 2018 , the Company was not subject to this covenant. Subject to customary grace periods and notice requirements, the ABL Facility also contains customary events of default. The Company was in compliance with all applicable covenants under the ABL Facility as of December 31, 2018 . Promissory Note In connection with the Asset Acquisition, the Company assumed a security agreement and promissory note, which had an outstanding balance of $0.8 million as of December 31, 2018 , all of which was classified as a current obligation. The amount owed in respect of the promissory note was originally used for the purchase of underground mining equipment and such note is secured by the same mining equipment. The promissory note matures on March 31, 2019 and bears a fixed interest rate of 4.00% per annum. The Company is required to make monthly payments of principal and interest during the term of the promissory note. Senior Secured Notes On November 2, 2017, the Company consummated a private offering (the “Offering”) of $350.0 million aggregate principal amount of 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. The Company used the net proceeds of approximately $340.0 million from the Offering, together with cash on hand of approximately $260.0 million , to pay a special cash dividend of approximately $600.0 million , or $11.21 per share, to all of its stockholders on a pro rata basis (the "November Special Dividend"). On March 1, 2018, the Company issued $125.0 million in aggregate principal amount of its 8.00% Senior Secured Notes due 2024 (the "New Notes") 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. The Company used the net proceeds of the offering of the New 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"). In connection with the issuance of the New Notes, the Company incurred transaction costs of $6.4 million for the year ended December 31, 2018 , which consists of legal fees and structuring fees, and is included in transaction and other expenses in the 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 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” and, together with the New Notes, the "Notes"), 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 May 1, 2018. The Notes are fully and unconditionally guaranteed on a joint and several basis by each of the Company's direct and indirect wholly-owned domestic restricted subsidiaries that are guarantors under the ABL Facility (subject to customary release provisions). At any time prior to November 1, 2020, the Company may redeem the Notes, in whole or in part, at a price equal to 100.00% of the principal amount of the Notes redeemed plus the Applicable Premium (as defined in the indenture governing the Notes) and accrued and unpaid interest, if any, to, but excluding, the applicable redemption date. The Notes are redeemable at the Company's option, in whole or in part, from time to time, on or after November 1, 2020, at redemption prices specified in the indenture, plus accrued and unpaid interest, if any, to, but excluding the redemption date. At any time on or prior to November 1, 2020, the Company may redeem up to 40% of the aggregate principal amount of the Notes with the proceeds of certain equity offerings, at a redemption price of 108.00% of the principal amount of the Notes, plus accrued and unpaid interest, if any, to but excluding the redemption date. The Company is also required to make offers to purchase the Notes (i) at a purchase price of 101.00% of the principal amount thereof in the event it experiences specific kinds of change of control triggering events, (ii) at a purchase price of 103.00% of the principal amount thereof prior to making certain restricted payments, and (iii) at a purchase price of 100.00% of the principal amount thereof in the event it makes certain asset sales or dispositions and does not reinvest the net proceeds therefrom or use such net proceeds to repay certain indebtedness, in each case, plus accrued and unpaid interest, if any, to, but excluding the date of purchase.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 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 $3.2 million for the year ended December 31, 2018 , $2.9 million for the year ended December 31, 2017 , $1.7 million for the nine months ended December 31, 2016 , and $0.3 million for the three months ended March 31, 2016 (Predecessor). The Predecessor also received revenue from coal sales to affiliates of the Parent that were not acquired in connection with the Asset Acquisition. The Predecessor recognized revenue from these affiliates of $1.4 million for the three months ended March 31, 2016 (Predecessor).

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 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 December 31, 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 December 31, 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 December 31, 2018 and December 31, 2017 , the Company had no liability recorded for minimum throughput requirements. Lease and Royalty Obligations The Company’s leases are primarily for mining equipment and automobiles. At December 31, 2018 and 2017, the total cost of assets under capital leases was $7.9 million and $9.9 million , respectively. Accumulated amortization on assets under capital leases was $2.1 million and $1.6 million as of December 31, 2018 and 2017, respectively. Amortization expense for capital leases is included in depreciation and depletion expense. Future minimum payments under non-cancellable capitalized leases as of December 31, 2018 were as follows (in thousands): Capitalized Leases 2019 $ 4,310 2020 172 2021 — 2022 — 2023 — Total 4,482 Less: amount representing interest (28 ) Present value of minimum lease payments $ 4,454 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 $101.0 million , $93.3 million , $17.5 million , and $ 3.6 million for the year ended December 31, 2018 , the year ended December 31, 2017 , the nine months ended December 31, 2016 , and the three months ended March 31, 2016 (Predecessor), respectively.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Stockholders' Equity	Stockholders' Equity 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. As of December 31, 2018 , the Company has repurchased 1,633,200 shares for approximately $38.0 million , leaving approximately $2.0 million of share repurchases authorized under the Stock Repurchase Program. 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 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. On August 8, 2018, certain stockholders of the Company sold 2,204,806 shares of the Company's common stock in a public secondary offering at a price to the underwriter of $25.40 per share. The Company did not receive any of the proceeds from the offering. We refer to these offerings herein collectively as the "Secondary Equity Offerings." In connection with the Secondary Equity Offerings, we incurred transaction costs of approximately $2.7 million for the twelve months ended December 31, 2018 , respectively.

Derivative Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 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 December 31, 2018 , the Company had natural gas swap contracts outstanding with notional amounts 2,100 million British thermal units maturing in the first quarter of 2019. As of December 31, 2017 , the Company had natural gas swap contracts outstanding with notional amounts totaling 8,400 million British thermal units maturing in the fourth quarter of 2018. 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 Statements of Operations. The Company records all derivative instruments at fair value and had a liability of $0.2 million related to natural gas swap contracts outstanding as of December 31, 2018 , which is included in other current liabilities, and $1.7 million as of December 31, 2017 included in prepaid expenses in the accompanying Balance Sheets.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 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): Successor Fair Value Measurements as of December 31, 2018 Using: Level 1 Level 2 Level 3 Total Liabilities: Natural gas swap contracts $ — $ 178 $ — $ 178 Successor 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 other assets or other liabilities measured at fair value on a recurring basis as of December 31, 2018 or December 31, 2017 . During the year ended December 31, 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 year ended December 31, 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 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 December 31, 2018 , there were no borrowings outstanding under the ABL Facility and there were $4.6 million of letters of credit issued and outstanding under the ABL Facility. The estimated fair value of the Notes is approximately $471.4 million based upon observable market data (Level 2). The carrying value of the Company's outstanding promissory note approximates its fair value.

Net Income (Loss) per Share

Net Income (Loss) per Share	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Net Income (Loss) per Share	Net Income (Loss) per Share The computation of basic net income (loss) per share is based on the number of weighted average common shares outstanding during the period. The computation of diluted net income (loss) per share is based on the weighted average number of shares outstanding plus the incremental shares that would be outstanding assuming issuance of restricted stock. The number of incremental shares is calculated by applying the treasury stock method. Basic and diluted net income (loss) per share was calculated as follows (in thousands, except per share data): Successor For the year ended For the year ended For the nine months ended December 31, 2018 2017 2016 Numerator: Net income (loss) $ 696,787 $ 455,046 $ (49,673 ) Denominator: Weighted-average shares used to compute net income (loss) per share—basic 52,812 52,800 52,640 Dilutive restricted stock awards and units 106 6 — Weighted-average shares used to compute net income (loss) per share—diluted 52,918 52,806 52,640 Net income (loss) per share—basic $ 13.19 $ 8.62 $ (0.94 ) Net income (loss) per share—diluted $ 13.17 $ 8.62 $ (0.94 ) As of December 31, 2018 , there were 88,809 shares of common stock issued under the 2016 Equity Plan to certain directors and employees, for which the service based vesting conditions were not met as of the measurement date and are included in dilutive earnings per share. There were 109,654 shares granted under the 2017 Equity Plan to certain directors and employees, for which neither the service based nor performance based vesting conditions were met as of the measurement date. As such, these shares have been excluded from basic and diluted earnings per share. As of December 31, 2018 , there were 43,580 shares of common stock contingently issuable upon the settlement of a vested phantom unit award under the 2016 Equity Plan and 13,157 shares of common stock contingently issuable upon the settlement of a vested restricted stock unit award under the 2017 Equity Plan. The settlement date is the earlier of a change in control as described in the 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 December 31, 2018 there were 44,265 shares of common stock issued under the 2017 Equity plan to certain directors and employees which immediately vested, but settle over the next two years on the anniversary of issuance. As such, these shares have been included in both basic and diluted earnings per share. As of December 31, 2018 , there were 17,182 shares of common stock issued under the 2017 Equity Plan to certain directors and employees for which the service based vesting conditions were not met as of the measurement date and are included in dilutive earnings per share. On March 31, 2017, the Company's board of managers declared a cash distribution of $3.56 per share, totaling $190.0 million, which was paid on March 31, 2017 to holders of Class A Units, Class B Units and Class C Units of record as of March 31, 2017. On May 17, 2017, the Board adopted the Dividend Policy of paying a quarterly cash dividend of $0.05 per share. The initial quarterly dividend of $2.7 million was paid on June 13, 2017 to stockholders of record on May 30, 2017. The Dividend Policy also states the following: In addition to the regular quarterly dividend and to the extent that the Company generates excess cash that is beyond the then current requirements of the business, the Board may consider returning all or a portion of such excess cash to stockholders through a special dividend or implementation of a stock repurchase program. Any future dividends or stock repurchases will be at the discretion of the Board and subject to consideration of a number of factors, including business and market conditions, future financial performance and other strategic investment opportunities. The Company will also seek to optimize its capital structure to improve returns to stockholders while allowing flexibility for the Company to pursue very selective strategic growth opportunities that can provide compelling stockholder returns. On July 31, 2017, the Board declared a regular quarterly cash dividend of $0.05 per share, totaling $2.7 million , which was paid on August 23, 2017, to stockholders of record as of the close of business on August 14, 2017. On October 25, 2017, the Board declared a regular quarterly cash dividend of $0.05 per share, totaling $2.7 million , which was paid on November 10, 2017, to stockholders of record as of the close of business on November 3, 2017. On November 2, 2017, the Board declared the November Special Dividend of approximately $600.0 million , which was funded with the net proceeds from the Notes Offering, together with cash on hand of approximately $260.0 million and was paid on November 22, 2017 to stockholders of record as of the close of business on November 13, 2017. On February 13, 2018, the Board declared a regular quarterly cash dividend of $0.05 per share, totaling $2.7 million , which was paid on March 2, 2018, to stockholders of record as of the close of business on February 23, 2018. On April 3, 2018, the Board declared the April Special Dividend of approximately $350.0 million , which was funded with the net proceeds from the offering of the New Notes due 2024, together with cash on hand of approximately $225.0 million , and was paid on April 20, 2018 to stockholders of record as of the close of business on April 13, 2018. On April 24, 2018, the Board declared a regular quarterly cash dividend of $0.05 per share, totaling approximately $2.7 million , which was paid on May 11, 2018, to stockholders of record as of the close of business on May 4, 2018. On July 24, 2018, the Board declared a regular quarterly cash dividend of $0.05 per share, totaling approximately $2.7 million, which was paid on August 10, 2018, to stockholders of record as of the close of business on August 3, 2018. On October 23, 2018, the Board declared a regular quarterly cash dividend of $0.05 per share, totaling approximately $2.7 million , which was paid on November 9, 2018 to stockholders of record as of the close of business on November 2, 2018. On February 19, 2019, the Board declared a regular quarterly cash dividend of $0.05 per share, totaling $2.6 million , which will be paid on March 11, 2019, to stockholders of record as of the close of business on March 4, 2019.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 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): Successor Predecessor For the year ended December 31, For the year ended December 31, For the nine For the three 2018 2017 2016 2016 Revenues Mining $ 1,342,683 $ 1,124,645 $ 276,560 $ 65,154 All other 35,324 44,447 21,074 6,229 Total revenues $ 1,378,007 $ 1,169,092 $ 297,634 $ 71,383 Successor Predecessor For the year ended December 31, For the year ended December 31, For the nine For the year ended December 31, 2018 2017 2016 2016 Capital Expenditures Mining $ 97,607 $ 89,700 $ 9,342 $ 4,588 All other 4,013 2,925 2,189 834 Total capital expenditures $ 101,620 $ 92,625 $ 11,531 $ 5,422 The Company evaluates the performance of its segment based on Segment Adjusted EBITDA, which is defined as net income (loss) adjusted for other revenues, cost of other revenues, depreciation and depletion, selling, general and administrative, other postretirement benefits, 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 (loss), which is its most directly comparable financial measure calculated and presented in accordance with GAAP (in thousands): Successor Predecessor For the year ended December 31, For the year ended December 31, For the nine For the three 2018 2017 2016 2016 Segment Adjusted EBITDA $ 626,038 $ 532,115 $ 31,837 $ (7,143 ) Other revenues 35,324 44,447 21,074 6,229 Cost of other revenues (10,172 ) (28,422 ) (19,367 ) (4,698 ) Depreciation and depletion (97,209 ) (75,413 ) (47,413 ) (28,958 ) Selling, general and administrative (36,626 ) (36,453 ) (20,507 ) (9,008 ) Other postretirement benefits — — — (6,160 ) Restructuring charges — — — (3,418 ) Transaction and other costs (9,068 ) (12,873 ) (13,568 ) — Interest expense, net (37,314 ) (6,947 ) (1,711 ) (16,562 ) Reorganization items, net — — — 7,920 Gain on extinguishment of debt — — — — Income tax benefit (expense) 225,814 38,592 (18 ) (18 ) Net income (loss) $ 696,787 $ 455,046 $ (49,673 ) $ (61,816 )

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Regular Quarterly Dividend On February 19, 2019, the Board declared a regular quarterly cash dividend of $0.05 per share, totaling $2.6 million , which will be paid on March 11, 2019, to stockholders of record as of the close of business on March 4, 2019. Restricted Payment Offer and Concurrent Tender Offer On February 21, 2019, the Company announced the commencement of an offer to repurchase (the "Restricted Payment Offer") up to $150.0 million aggregate principal amount of its 8.00% Senior Secured Notes due 2024 (the “Notes”) at a repurchase price of 103% of the principal amount plus accrued and unpaid interest to the repurchase date. The Restricted Payment Offer is being made in accordance with the indenture governing the Notes to provide the Company with the ability in the future to declare special dividends and/or repurchase shares of common stock of an estimated $150 million . The Company concurrently announced the launch of a tender offer (the “Tender Offer”) to repurchase up to $150 million aggregate principal amount of its Notes, at a repurchase price of 104.25% of the principal amount plus accrued and unpaid interest to the repurchase date. This Annual Report on Form 10-K is not an offer to purchase or a solicitation of an offer to sell the Notes in the Restricted Payment Offer or the Tender Offer.

Supplemental Quarterly Financia

Supplemental Quarterly Financial Information (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Supplemental Quarterly Financial Information (Unaudited)	SUPPLEMENTAL SUMMARY QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (in thousands, except per share amounts) Quarter Ended Successor Fiscal Year 2018 March 31 June 30 September 30 December 31 Total revenues $ 421,788 $ 322,555 $ 273,304 $ 360,360 Gross profit (1) $ 223,328 $ 136,674 $ 99,412 $ 191,776 Operating income $ 187,254 $ 101,096 $ 62,719 $ 157,218 Net income (2) $ 178,694 $ 91,312 $ 52,591 $ 374,190 Net income per share—basic $ 3.36 $ 1.72 $ 1.00 $ 7.13 Net income per share—diluted $ 3.36 $ 1.72 $ 1.00 $ 7.11 Quarter Ended Successor Fiscal Year 2017 March 31 June 30 September 30 December 31 Total revenues $ 253,964 $ 363,370 $ 311,955 $ 239,803 Gross profit (1) $ 139,641 $ 195,423 $ 115,406 $ 97,670 Operating income (loss) $ 110,853 $ 163,276 $ 82,770 $ 66,502 Net income (loss) (3) $ 108,308 $ 129,865 $ 119,717 $ 97,156 Net income (loss) per share—basic and diluted (4) 2.06 $ 2.46 $ 2.27 $ 1.83 (1) Represents total revenues less cost of sales (exclusive of items shown separately below) and cost of other revenues (exclusive of items shown separately below) for each respective period. (2) Net income included transaction and other costs of $3.3 million , $1.0 million , $3.3 million , and $1.5 million for the three months ended March 31, 2018, June 30, 2018, September 30, 2018, and December 31, 2018. Net income for the three months ended December 31, 2018 also includes the impact of the NOL valuation allowance release discussed further in Note 8 and a change in the ARO due to revisions to estimates discussed further in Note 9. (3) Net income included transaction and other costs of $9.0 million and $3.8 million for the three months ended March 31, 2017 and June 30, 2017. Net income for the three months ended December 31, 2017 also includes the impact of the enactment of the Tax Cuts and Jobs Act. (4) The sum of quarterly EPS amounts may be different than annual amounts as a result of the impact of variations in shares outstanding.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	The accompanying financial statements have been presented on a consolidated basis for the “Successor” periods subsequent to the Asset Acquisition, which include the year ended December 31, 2018 , the year ended December 31, 2017 , and the nine months ended December 31, 2016, and on a combined basis for the “Predecessor” periods prior to the Asset Acquisition, which includes the three months ended March 31, 2016. The financial information of the Company has been separated by a vertical line on the face of the financial statements to identify these different bases of accounting for Predecessor and Successor periods.
Use of Estimates	Use of Estimates The Company prepares its financial statements in conformity with GAAP, which requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the periods presented. Due to the inherent uncertainty involved in making estimates, actual results could differ from those estimates.
Concentrations of Credit Risk and Major Customers	Concentrations of Credit Risk and Major Customers Credit is extended based on an evaluation of the individual customer’s financial condition. In some instances, the Company requires letters of credit, cash collateral or prepayments from its customers on or before shipment to mitigate the risk of loss.
Revenue Recognition	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 applied the standard to all customer contracts entered into as of the date of initial application. The Company concluded that the adoption did not change the timing at which the Company historically recognized revenue nor did it have a material impact on its consolidated financial statements. For periods prior to January 1, 2018, revenue was recognized when the following criteria had been met: (i) persuasive evidence of an arrangement existed; (ii) the price to the buyer was fixed or determinable; (iii) delivery had occurred; and (iv) collectability was 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 23. Our coal and gas sales generally include up to 45-day payment terms following the transfer of control of the goods to the customer. We typically do not include extended payment terms in our contracts with customers.
Shipping and Handling	Shipping and Handling Costs incurred to transport coal to the point of sale at the Port of Mobile, Alabama, are included in cost of sales and the gross amounts billed to customers, if any, to cover shipping and handling to the ultimate/final destination are included in sales.
Cash and Cash Equivalents and Restricted Cash	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 December 31, 2018 and December 31, 2017 , restricted cash included in other long-term assets in the Balance Sheet represents amounts invested in certificate of deposits as financial assurance for post mining reclamation obligations.
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.
Inventories	Inventories Inventories are valued at the lower of cost or net realizable value. Coal inventory costs include labor, supplies, equipment costs, operating overhead, freight, royalties, depreciation and depletion and other related costs. Coal inventories are valued using the first-in, first-out (“FIFO”) inventory valuation method. The valuation of coal inventories is subject to estimates due to possible gains and losses resulting from inventory movements from the mine site to storage facilities, inherent inaccuracies in belt scales and aerial surveys used to measure quantities and fluctuations in moisture content. Periodic adjustments to coal tonnages on hand are made for an estimate of coal shortages and overages due to these inherent gains and losses, primarily based on historical results from aerial surveys and periodic coal pile clean-ups. Supplies inventories are valued using the average cost method of accounting. Management evaluates its supplies inventory in terms of excess and obsolete exposures which includes such factors as anticipated usage, inventory turnover, inventory levels and ultimate market value. A reserve for excess and obsolete supplies inventory is established and charged to cost of sales in the Statements of Operations.
Deferred Longwall Move Expenses and Advanced Mining Royalties	Deferred Longwall Move Expenses Direct costs, including labor and supplies, associated with moving longwall equipment and the related equipment refurbishment costs are deferred and included in prepaid expenses. These deferred costs are amortized on a unit-of-production basis into cost of sales over the life of the subsequent panel of coal mined by the longwall equipment. See Note 5 for further disclosures related to deferred longwall move expenses. Advanced Mining Royalties Lease rights to coal reserves are often acquired in exchange for royalty payments. Advance mining royalties are advance payments made to lessors under terms of mineral lease agreements that are recoupable against future production royalties. These advance payments are deferred and charged to operations as the coal reserves are mined. Advance mining royalties are included in other long-term assets.
Property, Plant and Equipment	Property, Plant and Equipment Property, Plant and Equipment Property, plant and equipment are recorded at cost. Depreciation is recorded principally on the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized on the straight-line method over the lesser of the useful life of the improvement or the remaining lease term. Estimated useful lives used in computing depreciation expense range from three to ten years for machinery and equipment, and from fifteen to thirty years for land improvements and buildings. Well life is used to estimate the useful life for gas properties and related development, and mine life is used for amortizing mine development costs. Gains and losses upon disposition are reflected in the Statements of Operations in the period of disposition. Maintenance and repair expenditures are charged to cost of sales as incurred. Deferred Mine Development Costs of developing new underground mines and certain underground expansion projects are capitalized. Underground development costs, which are costs incurred to make the coal physically accessible, may include construction permits and licenses, mine design, construction of access roads, main entries, airshafts, roof protection and other facilities. Mine development costs are amortized primarily on a unit-of-production basis over the estimated reserve tons directly benefiting from the capital expenditures. Costs amortized during the production phase of a mine are capitalized into inventory and expensed to cost of sales as the coal is sold. Owned and Leased Mineral Interests Costs to obtain coal reserves and lease mineral rights are capitalized based on cost or the fair value at acquisition and depleted using the unit-of-production method over the life of proven and probable reserves. Lease agreements are generally long-term in nature (original terms range from 10 to 50 years) and substantially all of the leases contain provisions that allow for automatic extension of the lease term provided certain requirements are met. Depletion expense was $9.6 million , $ 9.4 million , and $4.5 million for the years ended December 31, 2018 and December 31, 2017 , and the nine months ended December 31, 2016 , respectively, and is included in depreciation and depletion in the accompanying Statements of Operations. There was no depletion expense recorded for the three months ended March 31, 2016 (Predecessor). Asset Retirement Obligations The Company has certain asset retirement obligations primarily related to mine closing reclamation costs, perpetual water care costs and other costs associated with dismantling and removing facilities. Asset retirement obligations are determined for each mine using various estimates and assumptions, including estimates of disturbed acreage as determined from engineering data, estimates of future costs to reclaim the disturbed acreage and the timing of related cash flows, discounted using a credit-adjusted, risk-free rate. The Company's asset retirement obligations also include estimates to reclaim gas well in accordance with the Oil and Gas Board of Alabama. On at least an annual basis, the Company reviews the entire asset retirement obligation liability and makes necessary adjustments for permit changes, the anticipated timing of mine closures, and revisions to cost estimates and productivity assumptions to reflect current experience. As changes in estimates occur, the carrying amount of the obligation and asset are revised to reflect the new estimate after applying the appropriate credit-adjusted, risk-free discount rate. The future costs of these obligations are accrued at the estimated fair value in the period in which it is incurred if a reasonable estimate of fair value can be made. The present value of the estimated asset retirement cost is capitalized as part of the carrying amount of the long-lived asset. For sites where there is no asset, expense or income is recognized for changes in estimates. Capitalized asset retirement costs are amortized on a unit-of-production basis over the estimated reserves. Accretion of the asset retirement obligation is recognized over time and generally will escalate over the life of the producing asset, typically as production declines. Accretion is included in cost of sales on the Statements of Operations. Accrued mine closing costs, perpetual care costs and reclamation costs and other costs of dismantling and removing facilities are regularly reviewed by management and revised for changes in future estimated costs and regulatory requirements, as necessary. For ongoing operations, adjustments to the liability result in an adjustment to the corresponding asset. For some operations, adjustments to the liability are recognized as income or expense in the period the adjustment is recorded as no asset was recorded to offset the liability established during purchase accounting as the operations were idle at that time. Any difference between the recorded obligation and the actual cost of reclamation is recorded in profit or loss in the period the obligation is settled. See Note 9 for further disclosures related to asset retirement obligations. Impairment of Long-Lived Assets Property, plant and equipment and other long-lived assets are reviewed for impairment at least annually or whenever events or changes in circumstances indicate that the book value of the asset may not be recoverable. The Company periodically evaluates whether events and circumstances have occurred that would indicate possible impairment. When impairment indicators exist, the Company uses an estimate of the future undiscounted cash flows of the related asset or asset group over the remaining life in measuring whether or not the asset values are recoverable. If the carrying amount of an asset or asset group exceeds its estimated future cash flows, impairment is recognized equal to the amount by which the carrying amount of the asset exceeds the fair value of the asset or asset group. Fair value is generally determined using market quotes, if available, or a discounted cash flow approach. The Company’s estimate of future undiscounted cash flows is based on assumptions including long-term met coal pricing forecasts, anticipated production volumes and mine operating costs for the life of the mine or estimated useful life of the asset.
Equity Award Compensation (Successor) and Stock-Based Compensation (Predecessor)	Equity Award Compensation (Successor) The Company accounts for equity award-based compensation to employees and non-employee/directors in accordance with ASC 718 requiring employee equity awards to be accounted for under the fair value method adjusted for estimated forfeitures rates based on historical experience. The Company recognizes compensation expense associated with equity awards for all awards made to employees as the requisite service, performance and market vesting conditions are met. The Company measures compensation expense based on the grant-date fair value of the awards calculated using a Black-Scholes or Monte Carlo valuation model. Compensation expense for equity awards with a service-only condition is recognized over the employee’s requisite service period using a graded vesting method. For awards with a performance condition that affects vesting, the performance condition is not considered in determining the award’s grant-date fair value; however, the performance conditions are considered when estimating the quantity of awards that are expected to vest. No compensation expense is recorded for awards with performance conditions until the performance condition is determined to be probable of achievement. For awards with a market condition that affects vesting, the market condition is considered in determining the award’s grant-date fair value. Compensation expense for awards with a market condition is recognized straight-line over the derived or implied service period. For awards with both performance and market conditions, the market condition is incorporated into the fair value of the award, while the performance condition impacts the timing of expense recognition. Compensation expense for equity awards is included in cost of sales (exclusive of items shown separately below) and selling, general and administrative in the accompanying Statements of Operations. Stock-Based Compensation (Predecessor) Prior to the Asset Acquisition, the Parent periodically granted stock-based awards to its employees and its board of directors. Stock-based compensation expenses related to these awards were allocated to the Predecessor based on the awards and terms previously granted to the employees of the Predecessor’s business units or subsidiaries as well as an allocation of the Parent’s corporate employee expenses. The Parent measured stock options and other stock-based awards granted to employees and directors based on the fair value on the date of the grant and recognized compensation expense for those awards, net of estimated forfeitures, over the requisite service period, which was generally the vesting period of the respective award. The Parent recognized compensation expense for only the portion of awards that were expected to vest. In developing a forfeiture rate estimate, the Parent considered its historical experience to estimate pre-vesting forfeitures for service-based awards. The impact of a forfeiture rate adjustment was recognized in full in the period of adjustment, and when the actual forfeiture rate was materially different from the estimate. The Parent used the Black-Scholes option pricing model to value stock option grants and also estimated forfeitures in calculating the expense related to stock-based compensation. The Parent used the Monte Carlo simulation to value its performance share units in calculating the expense related to stock-based compensation.
Deferred Financing Costs	Deferred Financing Costs The costs to obtain new debt financing or amend existing financing agreements are deferred and amortized to interest expense over the life of the related indebtedness or credit facility using the straight line method. As of December 31, 2018 and December 31, 2017 , respectively, there were $ 3.1 million and $ 2.2 million , respectively, of origination fees related to the ABL Facility (as defined below) in other long-term assets on the accompanying Balance Sheet. As of December 31, 2018 and December 31, 2017 there were $6.8 million and $ 7.8 million , respectively of unamortized deferred financing costs and debt discount, net, related to the Notes (as defined below), which is presented as a net deduction from the carrying amount of the debt recognized in the accompanying Balance Sheet.
Income Taxes	Income Taxes The Company records a tax provision for the expected tax effects of the reported results of operations. The provision for income taxes is determined using the asset and liability method, under which deferred tax assets and liabilities are recognized for the expected future tax impact of temporary differences between the financial reporting and tax bases of assets and liabilities, and for operating losses and tax credit carryforwards. Deferred income tax assets and liabilities are measured using the currently enacted tax rates that apply to taxable income in effect for the years in which those tax assets and liabilities are expected to be realized or settled. The Company records a valuation allowance to reduce deferred income tax assets to the amount that is believed more likely than not to be realized. When the Company concludes that all or part of the net deferred income tax assets are not realizable in the future, the Company makes an adjustment to the valuation allowance that is charged to earnings in the period that such determination was made. The Company recognizes tax benefits from uncertain tax positions only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities, based on the technical merits of the position. The tax benefits recognized in the financial statements from such positions are then measured based on the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement.
Fair Value Measurements	Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. A three level hierarchy has been established for valuing assets and liabilities based on how transparent (observable) the inputs are that are used to determine fair value, with the inputs considered most observable categorized as Level 1 and those that are the least observable categorized as Level 3. Hierarchy levels are defined as follows: Level 1: Quoted prices in active markets for identical assets and liabilities. Level 2: Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. Level 3: Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.
New Accounting Pronouncements	New Accounting Pronouncements In February 2016, the FASB issued Accounting Standards Update ("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 adopted this standard on January 1, 2019 using the modified retrospective approach. The Company has concluded that the adoption of this standard did not have a material impact on the Company's consolidated financial position and results of operations.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 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 Balance Sheets that sum to the total of the same such amounts shown in the Statements of Cash Flows (in thousands): Successor December 31, 2018 December 31, 2017 Cash and cash equivalents $ 205,577 $ 35,470 Restricted cash included in other long-term assets 828 794 Total cash and cash equivalents and restricted cash included in the Statements of Cash Flows $ 206,405 $ 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 Balance Sheets that sum to the total of the same such amounts shown in the Statements of Cash Flows (in thousands): Successor December 31, 2018 December 31, 2017 Cash and cash equivalents $ 205,577 $ 35,470 Restricted cash included in other long-term assets 828 794 Total cash and cash equivalents and restricted cash included in the Statements of Cash Flows $ 206,405 $ 36,264

Acquisition of the Predecessor

Acquisition of the Predecessor (Tables)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Schedule of Acquisition of the Predecessor	The following tables summarize the final purchase price allocation, including the applicable measurement-period adjustments made upon finalization during the first quarter of 2017 (in thousands): Final purchase price: Cash paid $ 50,830 Fair value of First Lien Obligations relinquished in exchange for net assets of the Predecessor 598,607 Total purchase price $ 649,437 Final fair values of assets acquired and liabilities assumed: Cash and cash equivalents $ 26,723 Trade and other receivables 14,358 Inventories 46,464 Prepaid expenses and other current assets 30,722 Mineral interests 144,224 Property, plant and equipment 533,441 Other long-term assets 28,865 Total assets 824,797 Accounts payable 10,470 Accrued expenses 12,843 Other current liabilities 24,044 Current debt 2,879 Long-term debt 5,758 Deferred income taxes 1,400 Other long-term liabilities 117,966 Total liabilities 175,360 Total fair value of net assets acquired $ 649,437
Supplemental Unaudited Pro Forma Financial Information	The following unaudited pro forma results of operations give effect to the Asset Acquisition as if it had occurred on January 1, 2015. This unaudited pro forma financial information should not be relied upon as necessarily being indicative of the historical results that would have been obtained if the Asset Acquisition had actually occurred on that date, nor the results of operations in the future. The supplemental unaudited pro forma financial information was adjusted to (i) reflect the impact of certain fair value adjustments, including an adjustment to depreciation and depletion expense as a result of a change in the basis of property, plant and equipment and mineral interests, (ii) eliminate historical interest expense related to the notes, loans and other debt that was not assumed by the Company as part of the Asset Acquisition, (iii) eliminate a gain on reorganization items associated with the Chapter 11 Cases and (iv) eliminate the Predecessor's historical other postretirement benefit expense associated with the Predecessor's historical other postretirement benefit obligations for retiree medical and life insurance benefits, which were not assumed by the Company. Successor For the year ended December 31, 2016 (in thousands) As (1) Pro forma (2) Revenue $ 297,634 $ 369,017 Net loss $ (49,673 ) $ (67,476 ) (1) Reflects nine months of Successor period operations. (2) Includes nine months of Successor period operations and three months of Predecessor period operations on a pro forma basis.

Inventories, net (Tables)

Inventories, net (Tables)	12 Months Ended
	Dec. 31, 2018
Inventory Disclosure [Abstract]
Schedule of Inventories, Net	Inventories, net are summarized as follows (in thousands): Successor December 31, 2018 December 31, 2017 Coal $ 32,854 $ 32,422 Raw materials, parts, supplies and other, net 23,865 21,872 Total inventories, net $ 56,719 $ 54,294

Prepaid Expenses and Other (Tab

Prepaid Expenses and Other (Tables)	12 Months Ended
	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Prepaid Expenses	Prepaid expenses and other consisted of the following (in thousands): Successor December 31, 2018 December 31, 2017 Deferred longwall move expenses $ 20,053 $ 19,600 Prepaid insurance 4,670 4,955 Prepaid deposits 692 1,043 Gas hedge asset — 1,664 Other 2,517 2,114 Total prepaid expenses and other $ 27,932 $ 29,376

Mineral Interests and Propert_2

Mineral Interests and Property, Plant and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Schedule of Property, Plant and Equipment	Property, plant and equipment are summarized as follows (in thousands): Successor December 31, 2018 December 31, 2017 Land $ 72,139 $ 72,882 Land improvements 18,083 11,444 Building and leasehold improvements 71,561 82,836 Mine development and infrastructure costs 3,567 308 Machinery and equipment 512,594 441,353 Construction in progress 46,814 39,671 Total 724,758 648,494 Less: Accumulated depreciation (184,443 ) (111,749 ) Property, plant and equipment, net $ 540,315 $ 536,745

Other Long-Term Assets (Tables)

Other Long-Term Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Long-Term Assets	Other long-term assets consisted of the following (in thousands): Successor December 31, 2018 December 31, 2017 Advance mining royalties $ 10,910 $ 10,342 Restricted cash 828 794 Other 9,301 7,306 Total other long-term assets $ 21,039 $ 18,442

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	Income tax expense (benefit) consisted of the following (in thousands): Successor Predecessor For the year ended For the year ended For the nine months ended For the three 2018 2017 2016 2016 Current Federal $ (2,776 ) $ (36,906 ) $ (526 ) $ — State — — — — (2,776 ) (36,906 ) (526 ) — Deferred Federal (176,141 ) (1,712 ) 542 16 State (46,897 ) 26 2 2 (223,038 ) (1,686 ) 544 18 Total $ (225,814 ) $ (38,592 ) $ 18 $ 18
Schedule of Effective Income Tax Rate Reconciliation	income tax expense (benefit) differs from the expected tax expense (benefit) (computed by multiplying the U.S. federal statutory rate of 21% in 2018 and 35% in both 2017 and 2016 by income before income taxes) as a result of the following (in thousands): Successor Predecessor For the year ended For the year ended For the nine months ended For the three 2018 2017 2016 2016 Income (loss) before income tax expense (benefit) $ 470,973 $ 416,454 $ (49,655 ) $ (61,798 ) Tax expense (benefit) at statutory tax rate 98,904 145,759 (17,379 ) (21,629 ) Effect of: Depletion (18,227 ) (25,212 ) — — Estimate of the Tax Cuts and Jobs Act impact (2,775 ) (38,592 ) — — State and local income tax, net of federal effect 14,897 9,620 (1,051 ) (1,615 ) Valuation allowance on deferred tax assets (312,493 ) (129,245 ) 14,460 22,204 Non-deductible transaction costs 566 4,506 4,318 — Impact of restructuring — — — 1,111 Other (6,686 ) (5,428 ) (330 ) (53 ) Tax expense (benefit) recognized $ (225,814 ) $ (38,592 ) $ 18 $ 18
Schedule of Deferred Tax Assets and Liabilities	Significant components of the Company's deferred income tax assets and liabilities were (in thousands): Successor December 31, 2018 December 31, 2017 Deferred income tax assets: Net operating loss and credit carryforwards $ 298,180 $ 395,526 Inventory 119 1,083 Asset retirement obligations 15,526 23,765 Black lung obligations 6,720 7,991 Accrued expenses 3,611 561 Other 2,767 197 Total 326,923 429,123 Less: valuation allowance for deferred income tax assets — (312,493 ) Net deferred income tax assets 326,923 116,630 Deferred income tax liabilities: Prepaid expenses (9,894 ) (9,416 ) Property, plant and equipment (92,361 ) (105,715 ) Other (1,888 ) (1,757 ) Total deferred income tax liabilities (104,143 ) (116,888 ) Net deferred income tax asset (liability) $ 222,780 $ (258 )
Roll Forward of Deferred Tax Asset Valuation Allowance	The following table shows the balance of our valuation allowance and the associated activity: Successor December 31, 2018 December 31, 2017 Beginning balance $ 312,493 $ 767,290 Addition/(Reduction) - current tax expense/(benefit) (86,679 ) (129,245 ) Reduction due to application of IRC Section 382 — (130,327 ) Estimate of Tax Cuts and Jobs Act impact — (195,225 ) Release $ (225,814 ) $ — Ending balance $ — $ 312,493

Asset Retirement Obligation (Ta

Asset Retirement Obligation (Tables)	12 Months Ended
	Dec. 31, 2018
Asset Retirement Obligation Disclosure [Abstract]
Schedule of Changes in Asset Retirement Obligations	Changes in the asset retirement obligations (“ARO”) were as follows (in thousands): Successor For the twelve months ended December 31, 2018 For the twelve months ended Balance at Beginning of Period $ 99,668 $ 99,148 ARO liability assumed in the Asset Acquisition — — Accretion expense 4,619 1,834 Revisions to estimates (42,064 ) (658 ) Obligations settled (399 ) (656 ) Balance at End of Period $ 61,824 $ 99,668

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2018
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following (in thousands): Successor December 31, 2018 December 31, 2017 Accrued wages and employee benefits $ 37,221 $ 24,832 Accrued operating expenses 20,383 17,203 Accrued royalties 8,617 9,185 Accrued freight 4,053 5,051 Accrued interest 6,333 4,589 Accrued non-income taxes 1,642 1,553 Other 4,093 4,291 Total accrued expenses $ 82,342 $ 66,704

Reorganization Items, Net (Tabl

Reorganization Items, Net (Tables)	12 Months Ended
	Dec. 31, 2018
Reorganizations [Abstract]
Schedule of Reorganization Items	The following table presents reorganization items (in thousands): Predecessor For the three months ended 2016 Professional fees (10,962 ) Rejected executory contracts, leases and other 18,882 Reorganization items, net $ 7,920

Equity Award Plans (Tables)

Equity Award Plans (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-based Compensation, Restricted Stock	A summary of activity related to restricted stock unit award grants under the 2017 Equity Incentive Plan during the year ended December 31, 2018 is as follows: Shares Weighted Average Grant Date Fair Value Non-vested at December 31, 2017 8,823 $ 18.51 Granted 201,512 $ 27.71 Forfeited (15,935 ) $ 27.92 Vested (2,875 ) $ 18.39 Outstanding at December 31, 2018 191,525 $ 27.30 The following table presents a summary of Restricted Shares granted under the 2016 Equity Plan for the year ended December 31, 2018 : Number of Restricted Class C Shares Weighted Average Grant Date Fair Value Non-vested at December 31, 2017 266,027 $ 21.34 Granted — Forfeited (18,362 ) $ 21.34 Vested (98,126 ) $ 21.34 Outstanding at December 31, 2018 149,539 $ 21.34
Schedule of Share-based Payment Award, Equity Instruments Other than Options, Valuation Assumptions	The pricing model incorporated the assumptions as presented in the following table, shown at their weighted average values: Successor For the year ended December 31, 2017 For the nine months ended December 31, 2016 Expected stock price volatility (a) 35% 25.25% Risk-free interest rate (b) 1.75% 1.25% Expected life (years) (c) 4.17 5.00 (a) The Company bases its expected volatility on a group of companies believed to be a representative peer group, selected based on industry and market capitalization. (b) The risk-free rate for periods within the expected term of the award is based on the U.S. Government Bond yield with a term equal to the awards' expected term on the date of grant. (c) Expected life represents the period of time that awards granted are expected to be outstanding.

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of Long-Term Debt	Debt consisted of the following (in thousands): December 31, 2018 December 31, 2017 Weighted Average Interest Rate at December 31, 2018 Final Maturity Senior secured notes $ 475,000 $ 350,000 8% 2024 Promissory note 760 3,725 4% 2019 Debt discount, net (6,769 ) (7,812 ) Total debt 468,991 345,913 Less: current debt (760 ) (2,965 ) Total long-term debt $ 468,231 $ 342,948
Schedule of Maturities of Long-term Debt	The Company's minimum debt repayment schedule, excluding interest, as of December 31, 2018 is as follows (in thousands): Payments Due 2019 2020 2021 2022 2023 Thereafter Senior secured notes $ — $ — $ — $ — $ — $475,000 Promissory note 760 — — — — — Total $ 760 $ — $ — $ — $ — $ 475,000

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments for Capital Leases	Future minimum payments under non-cancellable capitalized leases as of December 31, 2018 were as follows (in thousands): Capitalized Leases 2019 $ 4,310 2020 172 2021 — 2022 — 2023 — Total 4,482 Less: amount representing interest (28 ) Present value of minimum lease payments $ 4,454

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 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): Successor Fair Value Measurements as of December 31, 2018 Using: Level 1 Level 2 Level 3 Total Liabilities: Natural gas swap contracts $ — $ 178 $ — $ 178 Successor 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

Net Income (Loss) per Share (Ta

Net Income (Loss) per Share (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	Basic and diluted net income (loss) per share was calculated as follows (in thousands, except per share data): Successor For the year ended For the year ended For the nine months ended December 31, 2018 2017 2016 Numerator: Net income (loss) $ 696,787 $ 455,046 $ (49,673 ) Denominator: Weighted-average shares used to compute net income (loss) per share—basic 52,812 52,800 52,640 Dilutive restricted stock awards and units 106 6 — Weighted-average shares used to compute net income (loss) per share—diluted 52,918 52,806 52,640 Net income (loss) per share—basic $ 13.19 $ 8.62 $ (0.94 ) Net income (loss) per share—diluted $ 13.17 $ 8.62 $ (0.94 )

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Reconciliation of Revenue from Segments to Consolidated	The following tables include reconciliations of segment information to consolidated amounts (in thousands): Successor Predecessor For the year ended December 31, For the year ended December 31, For the nine For the three 2018 2017 2016 2016 Revenues Mining $ 1,342,683 $ 1,124,645 $ 276,560 $ 65,154 All other 35,324 44,447 21,074 6,229 Total revenues $ 1,378,007 $ 1,169,092 $ 297,634 $ 71,383
Reconciliation of Capital Expenditures from Segments to Consolidated	Successor Predecessor For the year ended December 31, For the year ended December 31, For the nine For the year ended December 31, 2018 2017 2016 2016 Capital Expenditures Mining $ 97,607 $ 89,700 $ 9,342 $ 4,588 All other 4,013 2,925 2,189 834 Total capital expenditures $ 101,620 $ 92,625 $ 11,531 $ 5,422
Reconciliation of Net Income (Loss) from Segments to Consolidated	Below is a reconciliation of Segment Adjusted EBITDA to net income (loss), which is its most directly comparable financial measure calculated and presented in accordance with GAAP (in thousands): Successor Predecessor For the year ended December 31, For the year ended December 31, For the nine For the three 2018 2017 2016 2016 Segment Adjusted EBITDA $ 626,038 $ 532,115 $ 31,837 $ (7,143 ) Other revenues 35,324 44,447 21,074 6,229 Cost of other revenues (10,172 ) (28,422 ) (19,367 ) (4,698 ) Depreciation and depletion (97,209 ) (75,413 ) (47,413 ) (28,958 ) Selling, general and administrative (36,626 ) (36,453 ) (20,507 ) (9,008 ) Other postretirement benefits — — — (6,160 ) Restructuring charges — — — (3,418 ) Transaction and other costs (9,068 ) (12,873 ) (13,568 ) — Interest expense, net (37,314 ) (6,947 ) (1,711 ) (16,562 ) Reorganization items, net — — — 7,920 Gain on extinguishment of debt — — — — Income tax benefit (expense) 225,814 38,592 (18 ) (18 ) Net income (loss) $ 696,787 $ 455,046 $ (49,673 ) $ (61,816 )

Supplemental Quarterly Financ_2

Supplemental Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Supplemental Quarterly Financial Information (Unaudited)	Quarter Ended Successor Fiscal Year 2018 March 31 June 30 September 30 December 31 Total revenues $ 421,788 $ 322,555 $ 273,304 $ 360,360 Gross profit (1) $ 223,328 $ 136,674 $ 99,412 $ 191,776 Operating income $ 187,254 $ 101,096 $ 62,719 $ 157,218 Net income (2) $ 178,694 $ 91,312 $ 52,591 $ 374,190 Net income per share—basic $ 3.36 $ 1.72 $ 1.00 $ 7.13 Net income per share—diluted $ 3.36 $ 1.72 $ 1.00 $ 7.11 Quarter Ended Successor Fiscal Year 2017 March 31 June 30 September 30 December 31 Total revenues $ 253,964 $ 363,370 $ 311,955 $ 239,803 Gross profit (1) $ 139,641 $ 195,423 $ 115,406 $ 97,670 Operating income (loss) $ 110,853 $ 163,276 $ 82,770 $ 66,502 Net income (loss) (3) $ 108,308 $ 129,865 $ 119,717 $ 97,156 Net income (loss) per share—basic and diluted (4) 2.06 $ 2.46 $ 2.27 $ 1.83 (1) Represents total revenues less cost of sales (exclusive of items shown separately below) and cost of other revenues (exclusive of items shown separately below) for each respective period. (2) Net income included transaction and other costs of $3.3 million , $1.0 million , $3.3 million , and $1.5 million for the three months ended March 31, 2018, June 30, 2018, September 30, 2018, and December 31, 2018. Net income for the three months ended December 31, 2018 also includes the impact of the NOL valuation allowance release discussed further in Note 8 and a change in the ARO due to revisions to estimates discussed further in Note 9. (3) Net income included transaction and other costs of $9.0 million and $3.8 million for the three months ended March 31, 2017 and June 30, 2017. Net income for the three months ended December 31, 2017 also includes the impact of the enactment of the Tax Cuts and Jobs Act. (4) The sum of quarterly EPS amounts may be different than annual amounts as a result of the impact of variations in shares outstanding.

Business and Basis of Present_2

Business and Basis of Presentation - Description of the Business (Details) - USD ($) $ in Billions	Nov. 05, 2015	Dec. 31, 2018	Apr. 01, 2011
Promissory note
Business Acquisition [Line Items]
Stated interest rate		4.00%
Predecessor
Business Acquisition [Line Items]
Credit bid to acquire business	$ 1.1
Walter Energy, Inc. | Promissory note | Senior Secured Notes due 2019
Business Acquisition [Line Items]
Stated interest rate			9.50%

Business and Basis of Present_3

Business and Basis of Presentation - Corporate Conversion and Initial Public Offering (Details) - USD ($) $ / shares in Units, $ in Millions	Apr. 19, 2017	Dec. 31, 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)		51,622,898	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

Business and Basis of Present_4

Business and Basis of Presentation - Predecessor Presentation (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Interest (expense), net			$ 37,314	$ 6,947
Gain on extinguishment of debt			$ 0	$ 0
Predecessor
Business Acquisition [Line Items]
Allocated costs	$ 7,800
Interest (expense), net	16,562	$ 1,711
Gain on extinguishment of debt	0	$ 0
Change in attribution of parent debt	$ 626

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Concentrations of Credit Risk and Major Customers (Details) - USD ($) $ in Thousands

3 Months Ended

9 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

Mar. 31, 2016

Dec. 31, 2016

Dec. 31, 2018

Dec. 31, 2017

Concentration Risk [Line Items]

Revenue

$ 360,360

$ 273,304

$ 322,555

$ 421,788

$ 239,803

$ 311,955

$ 363,370

$ 253,964

$ 297,634

$ 1,378,007

$ 1,169,092

Mining And Marketing Met Coal - Foreign Steel Customers | Sales Revenue, Net

Concentration Risk [Line Items]

Concentration risk, percentage

97.40%

Mining And Marketing Met Coal - Foreign Steel Customers | Trade Receivables

Concentration Risk [Line Items]

Concentration risk, percentage

95.60%

Customer Concentration Risk | Sales Revenue, Net | Xcoal Energy And Resources

Concentration Risk [Line Items]

Concentration risk, percentage

16.40%

15.10%

16.10%

Customer Concentration Risk | Sales Revenue, Net | Exiros BV Sucursal Uruguay

Concentration Risk [Line Items]

Concentration risk, percentage

11.00%

Customer Concentration Risk | Sales Revenue, Net | Salzgitter Flachstahl GmBH

Concentration Risk [Line Items]

Concentration risk, percentage

15.60%

10.00%

Customer Concentration Risk | Sales Revenue, Net | Voestelpine

Concentration Risk [Line Items]

Concentration risk, percentage

12.80%

12.70%

Customer Concentration Risk | Sales Revenue, Net | Huettenwerke Krupp Mannesmann GmBH

Concentration Risk [Line Items]

Concentration risk, percentage

12.30%

10.50%

Europe | Geographic Concentration Risk | Sales Revenue, Net

Concentration Risk [Line Items]

Concentration risk, percentage

55.00%

South America | Geographic Concentration Risk | Sales Revenue, Net

Concentration Risk [Line Items]

Concentration risk, percentage

31.00%

Asia | Geographic Concentration Risk | Sales Revenue, Net

Concentration Risk [Line Items]

Concentration risk, percentage

14.00%

Sales

Concentration Risk [Line Items]

Revenue

$ 1,342,683

$ 1,124,645

Sales | Customer Concentration Risk | Sales Revenue, Net | Xcoal Energy And Resources

Concentration Risk [Line Items]

Revenue

$ 10,700

203,600

181,900

Sales | Customer Concentration Risk | Sales Revenue, Net | Exiros BV Sucursal Uruguay

Concentration Risk [Line Items]

Revenue

148,500

Sales | Customer Concentration Risk | Sales Revenue, Net | Salzgitter Flachstahl GmBH

Concentration Risk [Line Items]

Revenue

$ 43,100

$ 112,800

Sales | Customer Concentration Risk | Sales Revenue, Net | Voestelpine

Concentration Risk [Line Items]

Revenue

$ 8,300

35,300

Sales | Customer Concentration Risk | Sales Revenue, Net | Huettenwerke Krupp Mannesmann GmBH

Concentration Risk [Line Items]

Revenue

$ 34,000

$ 141,300

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 205,577	$ 35,470
Restricted cash included in other long-term assets	828	794
Total cash and cash equivalents and restricted cash included in the Statements of Cash Flows	$ 206,405	$ 36,264	$ 152,656	$ 0

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Short-term Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 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 Accoun_7

Summary of Significant Accounting Policies - Owned and Leased Mineral Interests (Details) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Depletion		$ 4,500,000	$ 9,600,000	$ 9,400,000
Minimum
Property, Plant and Equipment [Line Items]
Mineral rights, lease term			10 years
Maximum
Property, Plant and Equipment [Line Items]
Mineral rights, lease term			50 years
Predecessor
Property, Plant and Equipment [Line Items]
Depletion	$ 0

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Deferred Financing Costs (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Revolving Credit Agreement | Citibank
Line of Credit Facility [Line Items]
Origination fees	$ 6.8	$ 7.8
Senior Secured Notes Due 2024 | Senior secured notes
Line of Credit Facility [Line Items]
Unamortized deferred financing costs and debt discount	$ 3.1	$ 2.2

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - New Accounting Pronouncements (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Decrease to additional paid in capital		$ 3,525
Predecessor
Business Acquisition [Line Items]
Decrease in fair value of mineral interests	$ 3,500
Decrease to additional paid in capital	$ 3,500

Acquisition of the Predecesso_2

Acquisition of the Predecessor (Details) - USD ($) $ in Thousands	Nov. 05, 2015	Mar. 31, 2018	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Cash receipt from escrow agreement			$ 9,364	$ 0	$ 0
Net cash paid in acquisition			24,107	$ 0	0
Decrease to additional paid in capital					$ 3,525
Predecessor
Business Acquisition [Line Items]
Cash paid	$ 50,830
Cash receipt from escrow agreement			$ 9,400
Net cash paid in acquisition	24,100
Cash acquired from acquisition	$ 26,700
Decrease in fair value of mineral interests		$ 3,500
Decrease to additional paid in capital		$ 3,500

Acquisition of the Predecesso_3

Acquisition of the Predecessor - Schedule of Business Acquisition (Details) - Predecessor $ in Thousands	Nov. 05, 2015USD ($)
Final purchase price:
Cash paid	$ 50,830
Fair value of First Lien Obligations relinquished in exchange for net assets of the Predecessor	598,607
Total purchase price	649,437
Final fair values of assets acquired and liabilities assumed:
Cash and cash equivalents	26,723
Trade and other receivables	14,358
Inventories	46,464
Prepaid expenses and other current assets	30,722
Mineral interests	144,224
Property, plant and equipment	533,441
Other long-term assets	28,865
Total assets	824,797
Accounts payable	10,470
Accrued expenses	12,843
Other current liabilities	24,044
Current debt	2,879
Long-term debt	5,758
Deferred income taxes	1,400
Other long-term liabilities	117,966
Total liabilities	175,360
Total fair value of net assets acquired	$ 649,437

Acquisition of the Predecesso_4

Acquisition of the Predecessor - Supplemental Unaudited Pro Forma Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended									9 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	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Revenue	$ 360,360	$ 273,304	$ 322,555	$ 421,788	$ 239,803	$ 311,955	$ 363,370	$ 253,964		$ 297,634	$ 1,378,007	$ 1,169,092
Net loss	$ 374,190	$ 52,591	$ 91,312	$ 178,694	$ 97,156	$ 119,717	$ 129,865	$ 108,308		(49,673)	$ 696,787	$ 455,046
Predecessor
Business Acquisition [Line Items]
Revenue									$ 71,383	297,634
Net loss									$ (61,816)	$ (49,673)
Predecessor
Business Acquisition [Line Items]
Revenue - Pro forma													$ 369,017
Net loss - Pro forma													$ (67,476)

Inventories, net (Details)

Inventories, net (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Coal	$ 32,854	$ 32,422
Raw materials, parts, supplies and other, net	23,865	21,872
Total inventories, net	$ 56,719	$ 54,294

Prepaid Expenses and Other (Det

Prepaid Expenses and Other (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred longwall move expenses	$ 20,053	$ 19,600
Prepaid insurance	4,670	4,955
Prepaid deposits	692	1,043
Gas hedge asset	0	1,664
Other	2,517	2,114
Total prepaid expenses and other	$ 27,932	$ 29,376

Mineral Interests and Propert_3

Mineral Interests and Property, Plant and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Mineral interests			$ 144,200	$ 144,200
Mineral properties, accumulated depletion			23,800	14,200
Depreciation and depletion		$ 47,413	$ 97,209	$ 75,413
Predecessor
Property, Plant and Equipment [Line Items]
Depreciation and depletion	$ 28,958	$ 47,413

Mineral Interests and Propert_4

Mineral Interests and Property, Plant and Equipment, Net - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 724,758	$ 648,494
Less: Accumulated depreciation	(184,443)	(111,749)
Property, plant and equipment, net	540,315	536,745
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	72,139	72,882
Land improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	18,083	11,444
Building and leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	71,561	82,836
Mine development and infrastructure costs
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	3,567	308
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	512,594	441,353
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 46,814	$ 39,671

Other Long-Term Assets (Details

Other Long-Term Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Advance mining royalties	$ 10,910	$ 10,342
Restricted cash	828	794
Other	9,301	7,306
Total other long-term assets	$ 21,039	$ 18,442

Income Taxes (Details)

Income Taxes (Details) - USD ($)	3 Months Ended		9 Months Ended	12 Months Ended
	Dec. 31, 2018	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Long-term income taxes receivable	$ 21,310,000			$ 21,310,000	$ 39,255,000
Income tax receivable recorded during period	(2,800,000)		$ 0	12,431,000	0
Income taxes receivable	21,607,000			21,607,000	9,176,000
Valuation allowance	0		767,290,000	0	312,493,000
Income (loss) before income tax expense (benefit)				470,973,000	416,454,000
Income tax (benefit) expense				(225,814,000)	(38,592,000)
Predecessor
Income Tax Disclosure [Line Items]
Income tax receivable recorded during period		$ 0
Income (loss) before income tax expense (benefit)		(61,798,000)	(49,655,000)
Income tax (benefit) expense		$ 18,000	18,000
Federal
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	1,100,000,000		1,900,000,000	1,100,000,000	1,600,000,000
State
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	1,200,000,000		$ 2,000,000,000	1,200,000,000	$ 1,600,000,000
General business credits
Income Tax Disclosure [Line Items]
General business credit carryforward	$ 11,500,000			$ 11,500,000

Income Taxes - Schedule of Inco

Income Taxes - Schedule of Income Tax Expense (Benefit) (Details) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Current
Federal			$ (2,776,000)	$ (36,906,000)
State			0	0
Total current income tax expense (benefit)			(2,776,000)	(36,906,000)
Deferred
Federal			(176,141,000)	(1,712,000)
State			(46,897,000)	26,000
Total deferred income tax expense (benefit)		$ 544,000	(223,038,000)	(1,686,000)
Income tax (benefit) expense			$ (225,814,000)	$ (38,592,000)
Predecessor
Current
Federal	$ 0	(526,000)
State	0	0
Total current income tax expense (benefit)	0	(526,000)
Deferred
Federal	16,000	542,000
State	2,000	2,000
Total deferred income tax expense (benefit)	18,000	544,000
Income tax (benefit) expense	$ 18,000	$ 18,000

Income Taxes - Income Tax Rate

Income Taxes - Income Tax Rate Reconciliation (Details) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Income (loss) before income tax expense (benefit)			$ 470,973,000	$ 416,454,000
Tax expense (benefit) at statutory tax rate			98,904,000	145,759,000
Effect of:
Depletion			(18,227,000)	(25,212,000)
Estimate of the Tax Cuts and Jobs Act impact			(2,775,000)	(38,592,000)
State and local income tax, net of federal effect			14,897,000	9,620,000
Valuation allowance on deferred tax assets			(312,493,000)	(129,245,000)
Non-deductible transaction costs			566,000	4,506,000
Impact of restructuring			0	0
Other			(6,686,000)	(5,428,000)
Income tax (benefit) expense			$ (225,814,000)	$ (38,592,000)
Predecessor
Income Tax Disclosure [Line Items]
Income (loss) before income tax expense (benefit)	$ (61,798,000)	$ (49,655,000)
Tax expense (benefit) at statutory tax rate	(21,629,000)	(17,379,000)
Effect of:
Depletion	0	0
Estimate of the Tax Cuts and Jobs Act impact	0	0
State and local income tax, net of federal effect	(1,615,000)	(1,051,000)
Valuation allowance on deferred tax assets	22,204,000	14,460,000
Non-deductible transaction costs	0	4,318,000
Impact of restructuring	1,111,000	0
Other	(53,000)	(330,000)
Income tax (benefit) expense	$ 18,000	$ 18,000

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred income tax assets:
Net operating loss and credit carryforwards	$ 298,180	$ 395,526
Inventory	119	1,083
Asset retirement obligations	15,526	23,765
Black lung obligations	6,720	7,991
Accrued expenses	3,611	561
Other	2,767	197
Total	326,923	429,123
Less: valuation allowance for deferred income tax assets	0	(312,493)	$ (767,290)
Net deferred income tax assets	326,923	116,630
Deferred income tax liabilities:
Prepaid expenses	(9,894)	(9,416)
Property, plant and equipment	(92,361)	(105,715)
Other	(1,888)	(1,757)
Total deferred income tax liabilities	(104,143)	(116,888)
Net deferred income tax asset (liability)	$ 222,780	$ (258)

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Asset Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Deferred Tax Asset Valuation Roll Forward
Beginning balance	$ 312,493	$ 767,290
Ending balance	0	312,493
Addition/(Reduction) - current tax expense/(benefit)
Deferred Tax Asset Valuation Roll Forward
Additions (reduction)	(86,679)	(129,245)
Reduction due to application of IRC Section 382
Deferred Tax Asset Valuation Roll Forward
Additions (reduction)	0	(130,327)
Estimate of Tax Cuts and Jobs Act impact
Deferred Tax Asset Valuation Roll Forward
Additions (reduction)	0	(195,225)
Release
Deferred Tax Asset Valuation Roll Forward
Additions (reduction)	$ (225,814)	$ 0

Asset Retirement Obligation - S

Asset Retirement Obligation - Schedule of Changes in Asset Retirement Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO, beginning balance	$ 99,668	$ 99,148
ARO liability assumed in the Asset Acquisition	0	0
Accretion expense	4,619	1,834
Revisions to estimates	(42,064)	(658)
Obligations settled	(399)	(656)
ARO, ending balance	$ 61,824	$ 99,668

Asset Retirement Obligation (De

Asset Retirement Obligation (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Asset retirement obligations, current	$ 2,775,000	$ 3,572,000
Asset retirement obligations, noncurrent	59,049,000	$ 96,096,000
Assets legally restricted to settle AROs	0
Adjustment to liability reflected in income	$ (24,600,000)
Adjustment to liability reflected in income (usd per share)	$ 0.47
Surety Bond
Loss Contingencies [Line Items]
Loss contingency	$ 44,400,000
Letter of Credit
Loss Contingencies [Line Items]
Loss contingency	2,100,000
Certificates of Deposit
Loss Contingencies [Line Items]
Loss contingency	$ 800,000

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued wages and employee benefits	$ 37,221	$ 24,832
Accrued operating expenses	20,383	17,203
Accrued royalties	8,617	9,185
Accrued freight	4,053	5,051
Accrued interest	6,333	4,589
Accrued non-income taxes	1,642	1,553
Other	4,093	4,291
Total accrued expenses	$ 82,342	$ 66,704

Reorganization Items, Net (Deta

Reorganization Items, Net (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Schedule of Reorganization Items [Line Items]
Reorganization items, net			$ 0	$ 0
Predecessor
Schedule of Reorganization Items [Line Items]
Professional fees	$ (10,962)
Rejected executory contracts, leases and other	18,882
Reorganization items, net	7,920	$ 0
Payments for reorganization items	$ 12,300

Restructuring Costs (Details)

Restructuring Costs (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring costs			$ 0	$ 0
Predecessor
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 3,418	$ 0
Predecessor | Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 3,400

Pneumoconiosis ("Black Lung")_2

Pneumoconiosis ("Black Lung") Obligations (Details) - USD ($) $ in Thousands	Apr. 01, 2016	Dec. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Short-term investments	$ 17,500
Black lung trust		$ 3,600	$ 4,000
Replacement option period	6 months
Estimated total black lung liabilities		26,800	31,900
Black lung obligations, current		1,600	1,700
Black lung obligations, noncurrent		$ 25,206	$ 30,208

Pension and Other Postretirem_2

Pension and Other Postretirement Benefits (Details) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2016USD ($)$ / h	Dec. 31, 2016USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2015
Defined Contribution Plan Disclosure [Line Items]
Other postretirement benefits			$ 0	$ 0
UMWA Collective Bargaining Agreement
Defined Contribution Plan Disclosure [Line Items]
Amount company agreed to contribute to plan			$ 25,000
Percent of company's employees represented			69.00%	69.00%
Successor Benefit Plan
Defined Contribution Plan Disclosure [Line Items]
Contributions to defined contribution plans		$ 1,100	$ 3,100	$ 1,400
Predecessor
Defined Contribution Plan Disclosure [Line Items]
Pension expense	$ 6,200
Other postretirement benefits	$ 6,160	$ 0
Predecessor | UMWA Collective Bargaining Agreement
Defined Contribution Plan Disclosure [Line Items]
Percent of company's employees represented					61.40%
Predecessor | Multiemployer Pension And Benefit Plans
Defined Contribution Plan Disclosure [Line Items]
Contribution rate per hour worked (usd per hour) | $ / h	8.16
Other postretirement benefits	$ 6,200

Equity Award Plans (Details)

Equity Award Plans (Details) - USD ($)	Aug. 08, 2018	Jun. 14, 2018	May 10, 2018	Jun. 01, 2017	Mar. 31, 2017	Jun. 30, 2018	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Apr. 12, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash distributions paid					$ 190,000,000
Common stock par value (in dollars per share)									$ 0.01	$ 0.01	$ 0.01
Assets held in trust									$ 5,400,000
Dividends paid								$ 0	360,635,000	$ 796,902,000
Equity award modification										1,255,000
Tranche Three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of dividends in cash				100.00%
Percentage of dividends in RSUs				100.00%
Tranche Four
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of dividends in cash				50.00%
Percentage of dividends in RSUs				50.00%
2017 Equity Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense									2,100,000
Unrecognized compensation expense									$ 1,500,000
Shares available for grant (in shares)									5,657,450
2016 Equity Plan Modification
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Conversion ratio				1
Dividends paid										200,000
Equity award modification										1,300,000
2016 Equity Plan Modification | Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage									33.00%
Vested amount				$ 100,000
2016 Equity Plan Modification | Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage									33.00%
Vested amount				$ 100,000
Vested percentage				50.00%
2016 Equity Plan Modification | Tranche Three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage									33.00%
Restricted Stock | 2016 Equity Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)									805,083
Forfeited (in shares)									25,335
Vested (in shares)									630,209
Excess income tax benefit										$ 3,400,000
Restricted Stock | 2016 Equity Plan | Tranche Six
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested (in shares)										532,083
Stock compensation expense										$ 3,200,000
Unrecognized compensation expense									$ 1,000,000
Restricted Stock | 2016 Equity Plan | Tranche Seven
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested (in shares)									98,126
Award vesting percentage									50.00%
Restricted Stock Units (RSUs) | 2017 Equity Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)									201,512
Forfeited (in shares)									15,935
Vested (in shares)									2,875
Director | Phantom Share Units (PSUs) | 2016 Equity Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)									43,580
Expiration period									5 years
Predecessor
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense							$ 400,000
Dividends paid							$ 0
August Equity Offering
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued in transaction (in shares)	2,204,806	5,000,000	8,000,000			13,000,000
Incremental stock compensation expense						$ 3,600,000
August Equity Offering | Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage									20.00%
August Equity Offering | Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage									20.00%
August Equity Offering | Tranche Three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage									20.00%
August Equity Offering | Tranche Four
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage									20.00%
August Equity Offering | Tranche Five
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage									20.00%

Equity Award Plans - Schedule o

Equity Award Plans - Schedule of Restricted Stock (Details)	12 Months Ended
	Dec. 31, 2018$ / sharesshares
2016 Equity Plan | Restricted Stock
Number of Restricted Class C Shares
Nonvested, beginning of period (in shares) | shares	266,027
Granted (in shares) | shares	0
Forfeited (in shares) | shares	(18,362)
Vested (in shares) | shares	(98,126)
Outstanding, end of period (in shares) | shares	149,539
Weighted Average Grant Date Fair Value
Nonvested, beginning of period (in dollars per share) | $ / shares	$ 21.34
Granted (in dollars per share) | $ / shares
Forfeited (in dollars per share) | $ / shares	21.34
Vested (in dollars per share) | $ / shares	21.34
Outstanding, end of period (in dollars per share) | $ / shares	$ 21.34
2017 Equity Plan | Restricted Stock Units (RSUs)
Number of Restricted Class C Shares
Nonvested, beginning of period (in shares) | shares	8,823
Granted (in shares) | shares	201,512
Forfeited (in shares) | shares	(15,935)
Vested (in shares) | shares	(2,875)
Outstanding, end of period (in shares) | shares	191,525
Weighted Average Grant Date Fair Value
Nonvested, beginning of period (in dollars per share) | $ / shares	$ 18.51
Granted (in dollars per share) | $ / shares	27.71
Forfeited (in dollars per share) | $ / shares	27.92
Vested (in dollars per share) | $ / shares	18.39
Outstanding, end of period (in dollars per share) | $ / shares	$ 27.30

Equity Award Plans - Fair Value

Equity Award Plans - Fair Value Assumptions (Details) - 2016 Equity Plan - Restricted Stock	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected stock price volatility	25.25%	35.00%
Risk-free interest rate	1.00%	1.75%
Expected life (years) (c)	5 years	4 years 2 months 1 day

Debt - Schedule of Long-Term De

Debt - Schedule of Long-Term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Debt discount, net	$ (6,769)	$ (7,812)
Long-term debt	468,991	345,913
Current portion of long-term debt	(760)	(2,965)
Total long-term debt	468,231	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	$ 760	$ 3,725
Long-term debt	$ 800
Weighted Average Interest Rate	4.00%

Debt - Minimum Debt Repayment S

Debt - Minimum Debt Repayment Schedule (Details) $ in Thousands	Dec. 31, 2018USD ($)
Debt Instrument [Line Items]
2,019	$ 760
2,020	0
2,021	0
2,022	0
2,023	0
Thereafter	475,000
Senior secured notes
Debt Instrument [Line Items]
2,019	0
2,020	0
2,021	0
2,022	0
2,023	0
Thereafter	475,000
Promissory note
Debt Instrument [Line Items]
2,019	760
2,020	0
2,021	0
2,022	0
2,023	0
Thereafter	$ 0

Debt - ABL Facility (Details)

Debt - ABL Facility (Details) - Citibank - Revolving Credit Agreement	12 Months Ended
	Dec. 31, 2018USD ($)	Oct. 15, 2018USD ($)	Oct. 03, 2017USD ($)
Line of Credit Facility [Line Items]
Amount outstanding	$ 0
Remaining borrowing capacity	$ 120,400,000
Coverage ratio	1
Swingline loan
Line of Credit Facility [Line Items]
Aggregate lender commitment			$ 10,000,000
Letter of credit
Line of Credit Facility [Line Items]
Aggregate lender commitment			$ 50,000,000
Amount outstanding	$ 4,600,000
Maximum
Line of Credit Facility [Line Items]
Aggregate lender commitment		$ 125,000,000

Debt - Promissory Note (Details

Debt - Promissory Note (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long-term debt	$ 468,991	$ 345,913
Current portion of long-term debt	760	$ 2,965
Promissory note
Debt Instrument [Line Items]
Long-term debt	$ 800
Stated interest rate	4.00%

Debt - Senior Secured Notes (De

Debt - Senior Secured Notes (Details) - USD ($)	Oct. 23, 2018	Jul. 24, 2018	Apr. 24, 2018	Apr. 20, 2018	Mar. 01, 2018	Feb. 13, 2018	Nov. 02, 2017	Oct. 25, 2017	Jul. 31, 2017	May 17, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Cash dividends	$ 2,700,000	$ 2,700,000	$ 2,700,000			$ 2,700,000		$ 2,700,000	$ 2,700,000	$ 2,700,000	$ 190,000,000
Dividends paid (in dollars per share)												$ 0	$ 6.73	$ 14.92
Debt issuance costs												$ 4,978,000	$ 3,713,000	$ 2,562,000
Senior Secured Notes Due 2024 | Anytime prior to November 1, 2020
Debt Instrument [Line Items]
Redemption price, percentage							100.00%
Senior Secured Notes Due 2024 | Upon occurrence of a change in control
Debt Instrument [Line Items]
Redemption price, percentage							101.00%
Senior Secured Notes Due 2024 | Prior to making certain restricted payments
Debt Instrument [Line Items]
Redemption price, percentage							103.00%
Senior Secured Notes Due 2024 | Upon occurrence of asset sales or dispositions
Debt Instrument [Line Items]
Redemption price, percentage							100.00%
Senior Secured Notes Due 2024, Partial Redemption | Anytime prior to November 1, 2020
Debt Instrument [Line Items]
Redemption price, percentage							108.00%
Percentage of aggregate principal amount redeemable							40.00%
Senior secured notes | Senior Secured Notes Due 2024
Debt Instrument [Line Items]
Face amount of debt							$ 350,000,000						$ 350,000,000
Stated interest rate							8.00%						8.00%
Net proceeds from debt							$ 340,000,000
Cash dividends							$ 600,000,000
Dividends paid (in dollars per share)							$ 11.21
Payment of special cash dividend							$ 260,000,000
Senior secured notes | Senior Secured Notes Due 2024, New Notes
Debt Instrument [Line Items]
Face amount of debt					$ 125,000,000
Stated interest rate					8.00%
Cash dividends				$ 350,000,000
Dividends paid (in dollars per share)				$ 6.53
Transaction costs													$ 6,400,000
Debt issuance costs					$ 3,700,000
Redemption price, percentage					103.00%
Payment of special cash dividend				$ 225,000,000

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Nov. 05, 2015
Predecessor | Affiliated Entity
Related Party Transaction [Line Items]
Revenue from related parties	$ 1.4
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		$ 1.7	$ 3.2	$ 2.9
Allocated Expenses to Joint Venture | Predecessor | Corporate Joint Venture
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 0.3

Commitments and Contingencies_2

Commitments and Contingencies (Details) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Guarantor Obligations [Line Items]
Total cost of assets under capital leases			$ 7,900,000	$ 9,900,000
Accumulated amortization on assets under capital lease			2,100,000	1,600,000
Coal royalty expense			101,000,000	93,300,000
Accrued expenses
Guarantor Obligations [Line Items]
Throughput obligation			$ 0	$ 0
Predecessor
Guarantor Obligations [Line Items]
Coal royalty expense	$ 3,600,000	$ 17,500,000

Commitments and Contingencies -

Commitments and Contingencies - Future Minimum Lease Payments on Capital Leases (Details) $ in Thousands	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,018	$ 4,310
2,019	172
2,020	0
2,021	0
2,022	0
Total	4,482
Less: amount representing interest	(28)
Present value of minimum lease payments	$ 4,454

Stockholders' Equity (Details)

Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	Aug. 08, 2018	Jun. 14, 2018	May 10, 2018	Jun. 30, 2018	Dec. 31, 2018	May 02, 2018
Class of Stock [Line Items]
Shares repurchased, value					$ 38,030
The Stock Repurchase Program
Class of Stock [Line Items]
Authorized amount						$ 40,000
Shares repurchased (in shares)			500,000		1,633,200
Shares repurchased, value					$ (38,000)
Remaining authorized repurchase amount					2,000
Aggregate amount of repurchase			$ 12,100
August Equity Offering
Class of Stock [Line Items]
Shares issued in transaction (in shares)	2,204,806	5,000,000	8,000,000	13,000,000
Price per share (in dollars per share)	$ 25.40	$ 28.35	$ 24.20
Secondary Equity Offerings
Class of Stock [Line Items]
Payments of stock issuance costs					$ 2,700

Derivative Instruments (Details

Derivative Instruments (Details) - Not Designated as Hedging Instrument - Natural gas swap contracts BTU in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)BTU	Dec. 31, 2017USD ($)BTU
Commodity Contract, Maturity Q4 2018
Derivative [Line Items]
Derivative energy measure (in BTUs) | BTU	2,100
Commodity Contract, Maturity Q4 2017
Derivative [Line Items]
Derivative energy measure (in BTUs) | BTU		8,400
Prepaid Expenses | Commodity Contract
Derivative [Line Items]
Derivative asset (liability) | $	$ 0.2
Other Current Liabilities | Commodity Contract
Derivative [Line Items]
Derivative asset (liability) | $		$ (1.7)

Fair Value of Financial Instr_3

Fair Value of Financial Instruments (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Measurements, Recurring | Commodity Contract | Natural gas swap contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset (liability)	$ (178,000)	$ 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]
Derivative asset (liability)	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]
Derivative asset (liability)	(178,000)	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]
Derivative asset (liability)	0	$ 0
Senior secured notes | Senior Secured Notes Due 2024 | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of long-term debt	471,400,000
Citibank | Revolving Credit Agreement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount outstanding	0
Citibank | Revolving Credit Agreement | Letter of credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount outstanding	$ 4,600,000

Net Income (Loss) per Share - S

Net Income (Loss) per Share - Schedule of Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								9 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, 2016	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net income (loss)	$ 374,190	$ 52,591	$ 91,312	$ 178,694	$ 97,156	$ 119,717	$ 129,865	$ 108,308	$ (49,673)	$ 696,787	$ 455,046
Denominator:
Weighted-average shares used to compute net income (loss) per share—basic (in shares)									52,640	52,812	52,800
Dilutive restricted stock awards and units (in shares)									0	106	6
Weighted-average shares used to compute net income (loss) per share—diluted (in shares)									52,640	52,918	52,806
Net income (loss) per share—basic (in dollars per share)	$ 7.13	$ 1	$ 1.72	$ 3.36					$ (0.94)	$ 13.19	$ 8.62
Net income (loss) per share—diluted (in dollars per share)	$ 7.11	$ 1	$ 1.72	$ 3.36					$ (0.94)	$ 13.17	$ 8.62

Net Income (Loss) per Share - N

Net Income (Loss) per Share - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions

Feb. 19, 2019

Oct. 23, 2018

Jul. 24, 2018

Apr. 24, 2018

Apr. 20, 2018

Feb. 13, 2018

Nov. 02, 2017

Oct. 25, 2017

Jul. 31, 2017

May 17, 2017

Mar. 31, 2017

Dec. 31, 2018

Dec. 31, 2017

Class of Stock [Line Items]

Dividends (in dollars per share)

$ 0.05

$ 0.05

$ 0.05

$ 0.05

$ 0.05

$ 0.05

$ 0.05

$ 3.56

Cash dividends

$ 2.7

$ 2.7

$ 2.7

$ 2.7

$ 2.7

$ 2.7

$ 2.7

$ 190

Restricted Stock | 2016 Equity Plan

Class of Stock [Line Items]

Vested (in shares)

630,209

Restricted Stock | 2017 Equity Plan

Class of Stock [Line Items]

Common stock issues to employees and directors, unvested (in shares)

17,182

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 issued (in shares)

43,580

Restricted Stock Units (RSUs) | 2017 Equity Plan

Class of Stock [Line Items]

Common stock issues to employees and directors, unvested (in shares)

191,525

8,823

Common stock shares issued (in shares)

13,157

Vested (in shares)

2,875

Restricted Stock | Restricted Stock | 2016 Equity Plan

Class of Stock [Line Items]

Antidilutive securities excluded from the computation of EPS

88,809

Restricted Stock | Restricted Stock | 2017 Equity Plan

Class of Stock [Line Items]

Antidilutive securities excluded from the computation of EPS

109,654

Senior Secured Notes Due 2024 | Senior secured notes

Class of Stock [Line Items]

Cash dividends

$ 600

Payment of special cash dividend

$ 260

Senior Secured Notes Due 2024, New Notes | Senior secured notes

Class of Stock [Line Items]

Cash dividends

$ 350

Payment of special cash dividend

$ 225

Subsequent Event

Class of Stock [Line Items]

Dividends (in dollars per share)

$ 0.05

Dividends payable

$ 2.6

Common Stock | 2017 Equity Plan

Class of Stock [Line Items]

Vested (in shares)

44,265

Segment Information (Details)

Segment Information (Details)	12 Months Ended
	Dec. 31, 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

9 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

Mar. 31, 2016

Dec. 31, 2016

Dec. 31, 2018

Dec. 31, 2017

Segment Reporting Information [Line Items]

Revenue

$ 360,360

$ 273,304

$ 322,555

$ 421,788

$ 239,803

$ 311,955

$ 363,370

$ 253,964

$ 297,634

$ 1,378,007

$ 1,169,092

Predecessor

Segment Reporting Information [Line Items]

Revenue

$ 71,383

297,634

Mining | Mining | Operating Segments

Segment Reporting Information [Line Items]

Revenue

1,342,683

1,124,645

Mining | Mining | Predecessor | Operating Segments

Segment Reporting Information [Line Items]

Revenue

65,154

276,560

All other

Segment Reporting Information [Line Items]

Revenue

35,324

44,447

All other | Segment Reconciling Items

Segment Reporting Information [Line Items]

Revenue

$ 35,324

$ 44,447

All other | Predecessor

Segment Reporting Information [Line Items]

Revenue

6,229

21,074

All other | Predecessor | Segment Reconciling Items

Segment Reporting Information [Line Items]

Revenue

$ 6,229

$ 21,074

Segment Information - Reconci_2

Segment Information - Reconciliation of Capital Expenditures (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Capital Expenditures		$ 11,531	$ 101,620	$ 92,625
Segment Reconciling Items
Segment Reporting Information [Line Items]
Capital Expenditures		2,189	4,013	2,925
Predecessor
Segment Reporting Information [Line Items]
Capital Expenditures	$ 5,422
Predecessor | Segment Reconciling Items
Segment Reporting Information [Line Items]
Capital Expenditures	834
Mining | Operating Segments
Segment Reporting Information [Line Items]
Capital Expenditures		$ 9,342	$ 97,607	$ 89,700
Mining | Predecessor | Operating Segments
Segment Reporting Information [Line Items]
Capital Expenditures	$ 4,588

Segment Information - Reconci_3

Segment Information - Reconciliation of Net Income (Loss) (Details) - USD ($)	3 Months Ended									9 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	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA											$ 626,038,000	$ 532,115,000
Revenue	$ 360,360,000	$ 273,304,000	$ 322,555,000	$ 421,788,000	$ 239,803,000	$ 311,955,000	$ 363,370,000	$ 253,964,000		$ 297,634,000	1,378,007,000	1,169,092,000
Cost of other revenues											(10,172,000)	(28,422,000)
Depreciation and depletion										(47,413,000)	(97,209,000)	(75,413,000)
Selling, general and administrative											(36,626,000)	(36,453,000)
Other postretirement benefits											0	0
Restructuring charges											0	0
Transaction and other costs	(1,500,000)	(3,300,000)	(1,000,000)	(3,300,000)			(3,800,000)	(9,000,000)			(9,068,000)	(12,873,000)
Interest expense, net											(37,314,000)	(6,947,000)
Reorganization items, net											0	0
Gain on extinguishment of debt											0	0
Income tax benefit (expense)											225,814,000	38,592,000
Net income (loss)	$ 374,190,000	$ 52,591,000	$ 91,312,000	$ 178,694,000	$ 97,156,000	$ 119,717,000	$ 129,865,000	$ 108,308,000		(49,673,000)	696,787,000	455,046,000
Predecessor
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA									$ (7,143,000)	31,837,000
Revenue									71,383,000	297,634,000
Cost of other revenues									(4,698,000)	(19,367,000)
Depreciation and depletion									(28,958,000)	(47,413,000)
Selling, general and administrative									(9,008,000)	(20,507,000)
Other postretirement benefits									(6,160,000)	0
Restructuring charges									(3,418,000)	0
Transaction and other costs									0	(13,568,000)
Interest expense, net									(16,562,000)	(1,711,000)
Reorganization items, net									7,920,000	0
Gain on extinguishment of debt									0	0
Income tax benefit (expense)									(18,000)	(18,000)
Net income (loss)									(61,816,000)	(49,673,000)
All other
Segment Reporting Information [Line Items]
Revenue											$ 35,324,000	$ 44,447,000
All other | Predecessor
Segment Reporting Information [Line Items]
Revenue									$ 6,229,000	$ 21,074,000

Subsequent Events (Details)

Subsequent Events (Details) - USD ($)	Feb. 21, 2019	Feb. 19, 2019	Oct. 23, 2018	Jul. 24, 2018	Apr. 24, 2018	Feb. 13, 2018	Oct. 25, 2017	Jul. 31, 2017	May 17, 2017	Mar. 31, 2017	Nov. 02, 2017
Subsequent Event [Line Items]
Dividends declared (in dollars per share)			$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 3.56
Subsequent Event
Subsequent Event [Line Items]
Dividends declared (in dollars per share)		$ 0.05
Dividends payable		$ 2,600,000
Restricted Payment Offer | Senior secured notes
Subsequent Event [Line Items]
Stated interest rate											8.00%
Restricted Payment Offer | Senior secured notes | Subsequent Event
Subsequent Event [Line Items]
Authorized amount of debt for repurchase	$ 150,000,000
Redemption price, percentage	103.00%
Tender Offer | Senior secured notes | Subsequent Event
Subsequent Event [Line Items]
Authorized amount of debt for repurchase	$ 150,000,000
Redemption price, percentage	104.25%
Common Stock | Subsequent Event
Subsequent Event [Line Items]
Estimated future common stock repurchased	$ 150,000,000

Supplemental Quarterly Financ_3

Supplemental Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								9 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, 2016	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 360,360	$ 273,304	$ 322,555	$ 421,788	$ 239,803	$ 311,955	$ 363,370	$ 253,964	$ 297,634	$ 1,378,007	$ 1,169,092
Gross profit	191,776	99,412	136,674	223,328	97,670	115,406	195,423	139,641
Operating income (loss)	157,218	62,719	101,096	187,254	66,502	82,770	163,276	110,853		508,287	423,401
Net income (loss)	$ 374,190	$ 52,591	$ 91,312	$ 178,694	$ 97,156	$ 119,717	$ 129,865	$ 108,308	$ (49,673)	$ 696,787	$ 455,046
Net income (loss) per share—basic (in dollars per share)	$ 7.13	$ 1	$ 1.72	$ 3.36					$ (0.94)	$ 13.19	$ 8.62
Net income (loss) per share—diluted (in dollars per share)	$ 7.11	$ 1	$ 1.72	$ 3.36					$ (0.94)	$ 13.17	$ 8.62
Net income (loss) per share—basic and diluted (in dollars per share)					$ 1.83	$ 2.27	$ 2.46	$ 2.06
Transaction and other costs	$ 1,500	$ 3,300	$ 1,000	$ 3,300			$ 3,800	$ 9,000		$ 9,068	$ 12,873

Uncategorized Items - hcc-20181

Label	Element	Value
Capital Lease Obligations Incurred	us-gaap_CapitalLeaseObligationsIncurred	$ 0
Liabilities Assumed	us-gaap_LiabilitiesAssumed1	175,360,000
Fair Value of Assets Acquired	us-gaap_FairValueOfAssetsAcquired	$ 828,321,000