Arch Resources (ARCH) 10-Q 31 Jul 18 2018 Q2 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 27, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	ARCH COAL INC
Entity Central Index Key	1,037,676
Document Type	10-Q
Document Period End Date	Jun. 30, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		19,587,748

Condensed Consolidated Income S

Condensed Consolidated Income Statements - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Revenues	$ 592,349	$ 549,866	$ 1,167,644	$ 1,150,841
Costs, expenses and other operating
Cost of sales (exclusive of items shown separately below)	474,388	434,465	929,168	894,915
Depreciation, depletion and amortization	30,549	30,701	60,252	62,622
Accretion on asset retirement obligations	6,993	7,623	13,985	15,246
Amortization of sales contracts, net	3,248	14,352	6,299	29,042
Change in fair value of coal derivatives and coal trading activities, net	15,138	863	11,724	1,717
Selling, general and administrative expenses	24,756	22,456	50,704	43,218
Other operating income, net	(7,318)	(3,518)	(14,250)	(5,828)
Costs, expenses and other operating	547,754	506,942	1,057,882	1,040,932
Income from operations	44,595	42,924	109,762	109,909
Interest expense, net
Interest expense	(5,050)	(6,003)	(10,445)	(15,428)
Interest and investment income	1,552	842	2,825	1,369
Interest expense, net	(3,498)	(5,161)	(7,620)	(14,059)
Income before nonoperating expenses	41,097	37,763	102,142	95,850
Nonoperating expenses
Non-service related pension and postretirement benefit (costs) credits	68	(232)	(1,235)	(953)
Net loss resulting from early retirement of debt and debt restructuring	(485)	(31)	(485)	(2,061)
Reorganization items, net	(740)	(21)	(1,041)	(2,849)
Nonoperating expenses	(1,157)	(284)	(2,761)	(5,863)
Income before income taxes	39,940	37,479	99,381	89,987
Provision for (benefit from) income taxes	(3,366)	319	(3,910)	1,159
Net income	$ 43,306	$ 37,160	$ 103,291	$ 88,828
Net income per common share
Basic earnings per common share (in dollars per share)	$ 2.15	$ 1.51	$ 5.03	$ 3.58
Diluted earnings per common share (in dollars per share)	$ 2.06	$ 1.48	$ 4.81	$ 3.52
Weighted average shares outstanding
Basic weighted average shares outstanding (in shares)	20,156	24,659	20,529	24,834
Diluted weighted average shares outstanding (in shares)	21,036	25,082	21,456	25,245
Dividends declared per common share (in dollars per share)	$ 0.4	$ 0.35	$ 0.8	$ 0.35

Condensed Consolidated Statemen

Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income	$ 43,306	$ 37,160	$ 103,291	$ 88,828
Derivative instruments
Comprehensive income (loss) before tax	(12,293)	257	(5,736)	276
Income tax benefit (provision)	0	0	0	0
Other comprehensive income (loss), derivative instruments, net of tax	(12,293)	257	(5,736)	276
Pension, postretirement and other post-employment benefits
Comprehensive income (loss) before tax	3,653	3,154	3,653	3,154
Income tax benefit (provision)	0	0	0	0
Other comprehensive income (loss), pension, postretirement and other post-employment benefits, net of tax	3,653	3,154	3,653	3,154
Available-for-sale securities
Comprehensive income (loss) before tax	177	0	(481)	(387)
Income tax benefit (provision)	0	0	0	0
Other comprehensive income (loss), available-for-sale securities, net of tax	177	0	(481)	(387)
Total other comprehensive income (loss)	(8,463)	3,411	(2,564)	3,043
Total comprehensive income	$ 34,843	$ 40,571	$ 100,727	$ 91,871

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 241,590	$ 273,387
Short term investments	160,894	155,846
Trade accounts receivable	198,362	172,604
Other receivables	12,612	29,771
Inventories	157,205	128,960
Other current assets	86,642	70,426
Total current assets	857,305	830,994
Property, plant and equipment, net	925,559	955,948
Other assets
Equity investments	104,189	106,107
Other noncurrent assets	62,360	86,583
Total other assets	166,549	192,690
Total assets	1,949,413	1,979,632
Current Liabilities
Accounts payable	131,027	134,137
Accrued expenses and other current liabilities	194,730	184,161
Current maturities of debt	12,533	15,783
Total current liabilities	338,290	334,081
Long-term debt	305,157	310,134
Asset retirement obligations	316,341	308,855
Accrued pension benefits	7,481	14,036
Accrued postretirement benefits other than pension	106,934	102,369
Accrued workers’ compensation	185,068	184,835
Other noncurrent liabilities	49,194	59,457
Total liabilities	1,308,465	1,313,767
Stockholders' equity
Common stock, $0.01 par value, authorized 300,000 shares, issued 25,047 shares at June 30, 2018 and December 31, 2017, respectively	250	250
Paid-in capital	708,127	700,125
Retained earnings	333,753	247,232
Treasury stock, 5,344 shares and 3,977 shares at June 30, 2018 and December 31, 2017, respectively, at cost	(418,985)	(302,109)
Accumulated other comprehensive income	17,803	20,367
Total stockholders’ equity	640,948	665,865
Total liabilities and stockholders’ equity	$ 1,949,413	$ 1,979,632

Condensed Consolidated Balance5

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Common stock, par value (in usd per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	25,047,000	25,047,000
Treasury stock, shares (in shares)	5,344,000	3,977,000

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities
Net income	$ 103,291	$ 88,828
Adjustments to reconcile to cash provided by operating activities:
Depreciation, depletion and amortization	60,252	62,622
Accretion on asset retirement obligations	13,985	15,246
Amortization of sales contracts, net	6,299	29,042
Prepaid royalties expensed	0	2,288
Deferred income taxes	8,730	5,996
Employee stock-based compensation expense	7,992	4,942
Gains on disposals and divestitures, net	131	(2,005)
Net loss resulting from early retirement of debt and debt restructuring	485	2,061
Amortization relating to financing activities	2,170	1,565
Changes in:
Receivables	(20,212)	(3,864)
Inventories	(28,245)	(23,594)
Accounts payable, accrued expenses and other current liabilities	(11,879)	(89)
Income taxes, net	11,560	(3,796)
Other	(9,563)	21,557
Cash provided by operating activities	144,996	200,799
Investing activities
Capital expenditures	(30,049)	(16,922)
Minimum royalty payments	(124)	(4,211)
Proceeds from disposals and divestitures	56	4,186
Purchases of short term investments	(110,359)	(157,364)
Proceeds from sales of short term investments	105,150	85,035
Investments in and advances to affiliates, net	0	(8,934)
Cash used in investing activities	(35,326)	(98,210)
Financing activities
Proceeds from issuance of term loan due 2024	0	298,500
Payments to extinguish term loan due 2021	0	(325,684)
Payments on term loan due 2024	(1,500)	(750)
Net payments on other debt	(7,307)	(5,207)
Debt financing costs	(529)	(8,900)
Net loss resulting from early retirement of debt and debt restructuring	(50)	(2,061)
Dividends paid	(16,333)	(8,563)
Purchases of treasury stock	(115,973)	(51,043)
Other	10
Cash used in financing activities	(141,682)	(103,708)
Decrease in cash and cash equivalents, including restricted cash	(32,012)	(1,119)
Cash and cash equivalents, including restricted cash, beginning of period	273,602	376,422
Cash and cash equivalents, including restricted cash, end of period	241,590	375,303
Cash and cash equivalents, including restricted cash, end of period
Cash and cash equivalents, including restricted cash	$ 273,602	$ 376,422

Basis of Presentation

Basis of Presentation	6 Months Ended
	Jun. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements include the accounts of Arch Coal, Inc. ("Arch Coal") and its subsidiaries (the “Company”). Unless the context indicates otherwise, the terms “Arch” and the “Company” are used interchangeably in this Quarterly Report on Form 10-Q. The Company’s primary business is the production of thermal and metallurgical coal from surface and underground mines located throughout the United States, for sale to utility, industrial and steel producers both in the United States and around the world. The Company currently operates mining complexes in West Virginia, Illinois, Wyoming and Colorado. All subsidiaries are wholly-owned. Intercompany transactions and accounts have been eliminated in consolidation. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States for interim financial reporting and U.S. Securities and Exchange Commission regulations. In the opinion of management, all adjustments, consisting of normal, recurring accruals considered necessary for a fair presentation, have been included. Results of operations for the three and six months ended June 30, 2018 are not necessarily indicative of results to be expected for the year ending December 31, 2018 . These financial statements should be read in conjunction with the audited financial statements and related notes as of and for the year ended December 31, 2017 included in the Company’s Annual Report on Form 10-K filed with the U.S. Securities and Exchange Commission.

Accounting Policies

Accounting Policies	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Accounting Policies	Accounting Policies Recently Adopted Accounting Guidance In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers.” ASU 2014-09 is a comprehensive revenue recognition standard that has superseded nearly all existing revenue recognition guidance under current U.S. GAAP and replaced it with a principle based approach for determining revenue recognition. ASU 2014-09 requires that companies recognize revenue based on the value of transferred goods or services as they occur in the contract. The ASU also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. ASU 2014-09 is effective for interim and annual periods beginning after December 15, 2017. The Company’s primary source of revenue is from the sale of coal through both short-term and long-term contracts with utilities, industrial customers and steel producers whereby revenue is currently recognized when risk of loss has passed to the customer. During the fourth quarter of 2017, the Company finalized its assessment related to the new standard by analyzing certain contracts representative of the majority of the Company’s coal sales and determined that the timing of revenue recognition related to the Company’s coal sales will remain consistent between the new standard and the previous standard. The Company also reviewed other sources of revenue, and concluded the current basis of accounting for these items is in accordance with the new standard. The Company adopted ASU 2014-09 effective January 1, 2018 using the modified retrospective method, and there was no cumulative adjustment to retained earnings. The Company also reviewed the disclosure requirements under the new standard and has compiled information needed for the expanded disclosures which are included within Note 18 , “ Revenue Recognition ” in the Condensed Consolidated Financial Statements. In August 2016, the FASB issued ASU 2016-15, “Classification of Certain Cash Receipts and Cash Payments.” The amendment requires the classification of certain cash receipts and cash payments in the statement of cash flows to reduce diversity in practice. The new guidance is effective for fiscal years beginning after December 15, 2017 and the interim periods therein, with early adoption permitted. The amendments in the classification should be applied retrospectively to all periods presented, unless deemed impracticable, in which case, the prospective application is permitted. The Company adopted ASU 2016-15 effective January 1, 2018 with no impact on the Company’s financial statements. In November 2016, FASB issued ASU 2016-18, “Statement of Cash Flows (Topic 230): Restricted Cash.” The ASU applies to all entities that have restricted cash or restricted cash equivalents and are required to present a statement of cash flows. The ASU requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. As a result, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning of period and end of period total amounts shown on the statement of cash flows. The ASU is effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. The ASU should be adopted using a retrospective transition method to each period presented. The Company adopted ASU 2016-18 effective January 1, 2018 and applied the ASU retrospectively to the periods presented in the Company's Condensed Consolidated Statements of Cash Flow. As a result, net cash used in investing activities for the six months ended June 30, 2017 was adjusted to exclude the change in restricted cash as follows: (in thousands) Six Months Ended June 30, 2017 Cash used in investing activities previously reported $ (68,915 ) Less: Withdrawals of restricted cash 29,295 Cash used in investing activities $ (98,210 ) In March 2017, the FASB issued ASU 2017-07, “Compensation-Retirement Benefits (Topic 715) Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost.” ASU 2017-07 changes the income statement presentation of defined benefit plan expense by requiring separation between operating expense (service cost component) and non-operating expense (all other components, including interest cost, amortization of prior service cost, curtailments and settlements, etc.). The operating expense component is reported with similar compensation costs while the non-operating components are reported in Nonoperating expense. In addition, only the service cost component is eligible for capitalization as part of an asset such as inventory or property, plant and equipment. The ASU is effective for public companies for fiscal years beginning after December 15, 2017, and interim periods therein. The ASU should be adopted using a retrospective transition method to each period presented. The Company adopted ASU 2017-07 effective January 1, 2018 and applied the ASU retrospectively to the periods presented in the Company's Condensed Consolidated Income Statements. The retrospective application resulted in a $0.6 million and $1.5 million reduction in cost of coal sales and a $0.3 million and $0.5 million increase in selling, general and administrative costs with the corresponding offset to Nonoperating expense for the three and six months ended June 30, 2017 . Recent Accounting Guidance Issued Not Yet Effective In February 2016, the FASB issued ASU 2016-02, “Leases” which, for operating leases, requires a lessee to recognize a right-of-use asset and a lease liability, initially measured at the present value of the lease payments, in its balance sheet. The standard also requires a lessee to recognize a single lease cost, calculated so that the cost of the lease is allocated over the term of the lease, on a generally straight line basis. The ASU is effective for public companies for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years; early adoption is permitted. The Company has both operating and capital leases. We expect the adoption of this standard to result in the recognition of right-of-use assets and lease liabilities not currently recorded on the Company’s financial statements. The Company is currently in the process of accumulating all contractual lease arrangements in order to determine the impact on its financial statements. 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 anticipates early adopting the standard in the third quarter of 2018, although we do not expect a significant impact to the Company’s financial results. In February 2018, the FASB issued ASU 2018-02, “Income Statement-Reporting Comprehensive Income (Topic 220) Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.” ASU 2018-02 provides an option to reclassify stranded tax effects within accumulated other comprehensive income to retained earnings due to the change in the U.S. federal tax rate in the Tax Cuts and Jobs Act of 2017. The ASU is effective for public companies for fiscal years beginning after December 15, 2018, and interim periods therein with early adoption permitted. The Company is currently in the process of analyzing the standard, but does not expect a significant impact to the Company’s financial statements.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income	6 Months Ended
	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income	Accumulated Other Comprehensive Income The following items are included in accumulated other comprehensive income ("AOCI"): Pension, Postretirement and Other Accumulated Post- Other Derivative Employment Available-for- Comprehensive Instruments Benefits Sale Securities Income (In thousands) Balance at December 31, 2017 $ 647 $ 19,720 $ — $ 20,367 Unrealized gains (losses) (5,248 ) 5,024 (465 ) (689 ) Amounts reclassified from AOCI (488 ) (1,371 ) (16 ) (1,875 ) Balance at June 30, 2018 $ (5,089 ) $ 23,373 $ (481 ) $ 17,803 The following amounts were reclassified out of AOCI: Three Months Ended June 30, Six Months Ended June 30, Details About AOCI Components 2018 2017 2018 2017 Line Item in the Condensed Consolidated Statement of Operations (In thousands) Coal hedges $ — $ — $ — $ — Revenues Interest rate hedges 348 — 488 — Interest expense — — — — Provision for (benefit from) income taxes $ 348 $ — $ 488 $ — Net of tax Pension, postretirement and other post-employment benefits Pension settlement 1,371 487 1,371 487 Non-service related pension and postretirement benefit (costs) credits 1,371 487 1,371 487 — — — — Provision for (benefit from) income taxes $ 1,371 $ 487 $ 1,371 $ 487 Net of tax Available-for-sale securities $ 16 $ — $ 16 $ 332 Interest and investment income — — — — Provision for (benefit from) income taxes $ 16 $ — $ 16 $ 332 Net of tax

Reorganization items, net

Reorganization items, net	6 Months Ended
	Jun. 30, 2018
Discontinued Operations and Disposal Groups [Abstract]
Reorganization items, net	Reorganization items, net In accordance with Accounting Codification Standard 852, “Reorganizations,” the income statement shall portray the results of operations of the reporting entity while it is in Chapter 11. Revenues, expenses (including professional fees), realized gains and losses, and provisions for losses resulting from reorganization and restructuring of the business shall be reported separately as reorganization items. During the three months ended June 30, 2018 and 2017 , the Company recorded $0.7 million and near $0.0 million , respectively in “Reorganization items, net” primarily comprised of professional fee expenses. Net cash paid for “Reorganization items, net” totaled $0.3 million and $0.9 million during the three months ended June 30, 2018 and 2017 , respectively. During the six months ended June 30, 2018 and 2017 , the Company recorded $1.0 million and $2.8 million , respectively in “Reorganization items, net” primarily comprised of professional fee expenses. Net cash paid for “Reorganization items, net” totaled $0.6 million and $4.7 million during the six months ended June 30, 2018 and 2017 , respectively.

Inventories

Inventories	6 Months Ended
	Jun. 30, 2018
Inventory Disclosure [Abstract]
Inventories	Inventories Inventories consist of the following: June 30, December 31, 2018 2017 (In thousands) Coal $ 72,268 $ 54,692 Repair parts and supplies 84,937 74,268 $ 157,205 $ 128,960 The repair parts and supplies are stated net of an allowance for slow-moving and obsolete inventories of $0.9 million at June 30, 2018 and $0.3 million at December 31, 2017 .

Investments in Available-for-Sa

Investments in Available-for-Sale Securities	6 Months Ended
	Jun. 30, 2018
Debt Securities, Available-for-sale [Abstract]
Investments in Available-for-Sale Securities	Investments in Available-for-Sale Securities The Company has invested in marketable debt securities, primarily highly liquid U.S. Treasury securities and investment grade corporate bonds. These investments are held in the custody of a major financial institution. These securities are classified as available-for-sale securities and, accordingly, the unrealized gains and losses are recorded through other comprehensive income. The Company’s investments in available-for-sale marketable securities are as follows: June 30, 2018 Balance Sheet Classification Gross Unrealized Fair Short-Term Other Cost Basis Gains Losses Value Investments Assets (In thousands) Available-for-sale: U.S. government and agency securities $ 88,858 $ 3 $ (161 ) $ 88,700 $ 88,700 $ — Corporate notes and bonds 72,516 3 (325 ) 72,194 72,194 — Total Investments $ 161,374 $ 6 $ (486 ) $ 160,894 $ 160,894 $ — December 31, 2017 Balance Sheet Classification Gross Unrealized Fair Short-Term Other Cost Basis Gains Losses Value Investments Assets (In thousands) Available-for-sale: U.S. government and agency securities $ 64,151 $ 22 $ (73 ) $ 64,100 $ 64,100 $ — Corporate notes and bonds 92,038 — (292 ) 91,746 91,746 — Total Investments $ 156,189 $ 22 $ (365 ) $ 155,846 $ 155,846 $ — The aggregate fair value of investments with unrealized losses that were owned for less than a year was $128.1 million and $132.0 million at June 30, 2018 and December 31, 2017 , respectively. The aggregate fair value of investments with unrealized losses that were owned for over a year was $17.5 million and $0.0 million at June 30, 2018 and December 31, 2017 , respectively. The unrealized losses in the Company’s portfolio at June 30, 2018 are the result of normal market fluctuations. The Company does not currently intend to sell these investments before recovery of their amortized cost base. The debt securities outstanding at June 30, 2018 have maturity dates ranging from the third quarter of 2018 through the fourth quarter of 2019 . The Company classifies its investments as current based on the nature of the investments and their availability to provide cash for use in current operations.

Sales Contracts

Sales Contracts	6 Months Ended
	Jun. 30, 2018
Acquired Sales Contracts [Abstract]
Sales Contracts	Sales Contracts The sales contracts reflected in the Condensed Consolidated Balance Sheets are as follows: June 30, 2018 December 31, 2017 Assets Liabilities Net Total Assets Liabilities Net Total (In thousands) (In thousands) Original fair value $ 97,196 $ 31,742 $ 97,196 $ 31,742 Accumulated amortization (91,650 ) (30,570 ) (84,760 ) (29,979 ) Total $ 5,546 $ 1,172 $ 4,374 $ 12,436 $ 1,763 $ 10,673 Balance Sheet classification: Other current $ 5,544 $ 634 $ 12,432 $ 934 Other noncurrent $ 2 $ 538 $ 4 $ 829 The Company anticipates the majority of the remaining net book value of sale contracts to be amortized in 2018 based upon expected shipments.

Derivatives

Derivatives	6 Months Ended
	Jun. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives	Derivatives Interest rate risk management The Company has entered into interest rate swaps to reduce the variability of cash outflows associated with interest payments on its variable rate term loan. These swaps have been designated as cash flow hedges. For additional information on these arrangements, see Note 10 , “ Debt and Financing Arrangements ,” in the Condensed Consolidated Financial Statements. Diesel fuel price risk management The Company is exposed to price risk with respect to diesel fuel purchased for use in its operations. The Company anticipates purchasing approximately 40 to 47 million gallons of diesel fuel for use in its operations during 2018 . To protect the Company’s cash flows from increases in the price of diesel fuel for its operations, the Company uses forward physical diesel purchase contracts and purchased heating oil call options. At June 30, 2018 , the Company had protected the price of approximately 70% of its expected diesel fuel purchases for the remainder of 2018 at an average strike price of $2.10 per gallon. Additionally, the Company has protected approximately 50% of its expected first half 2019 purchases with call options with an average strike price of $2.33 per gallon. At June 30, 2018 , the Company had outstanding heating oil call options for approximately 26 million gallons for the purpose of managing the price risk associated with future diesel purchases. These positions are not designated as hedges for accounting purposes, and therefore, changes in the fair value are recorded immediately to earnings. Coal price risk management positions The Company may sell or purchase forward contracts, swaps and options in the over-the-counter coal market in order to manage its exposure to coal prices. The Company has exposure to the risk of fluctuating coal prices related to forecasted, index-priced sales or purchases of coal or to the risk of changes in the fair value of a fixed price physical sales contract. Certain derivative contracts may be designated as hedges of these risks. At June 30, 2018 , the Company held derivatives for risk management purposes that are expected to settle in the following years: (Tons in thousands) 2018 2019 Total Coal sales 1,089 1,587 2,676 Coal purchases 433 79 512 The Company has also entered into a minimal quantity of natural gas put options to protect the Company from decreases in natural gas prices, which could impact thermal coal demand. These options are not designated as hedges. Coal trading positions The Company may sell or purchase forward contracts, swaps and options in the over-the-counter coal market for trading purposes. The Company is exposed to the risk of changes in coal prices on the value of its coal trading portfolio. The estimated future realization of the value of the trading portfolio is $0.4 million of losses during the remainder of 2018 and an immaterial amount of gains during 2019 . Tabular derivatives disclosures The Company has master netting agreements with all of its counterparties which allow for the settlement of contracts in an asset position with contracts in a liability position in the event of default or termination. Such netting arrangements reduce the Company’s credit exposure related to these counterparties. For classification purposes, the Company records the net fair value of all the positions with a given counterparty as a net asset or liability in the Condensed Consolidated Balance Sheets. The amounts shown in the table below represent the fair value position of individual contracts, and not the net position presented in the accompanying Condensed Consolidated Balance Sheets. The fair value and location of derivatives reflected in the accompanying Condensed Consolidated Balance Sheets are as follows: June 30, 2018 December 31, 2017 Fair Value of Derivatives Asset Liability Asset Liability (In thousands) Derivative Derivative Derivative Derivative Derivatives Designated as Hedging Instruments Coal $ 1,763 $ (9,388 ) $ 942 $ (2,146 ) Derivatives Not Designated as Hedging Instruments Heating oil -- diesel purchases 6,652 — 5,354 — Coal -- held for trading purposes 35,894 (36,323 ) 44,088 (45,221 ) Coal -- risk management 6,058 (22,900 ) 5,139 (9,892 ) Natural gas 42 — 27 — Total 48,646 (59,223 ) 54,608 (55,113 ) Total derivatives 50,409 (68,611 ) 55,550 (57,259 ) Effect of counterparty netting (42,542 ) 42,542 (50,042 ) 50,042 Net derivatives as classified in the balance sheets $ 7,867 $ (26,069 ) $ (18,202 ) $ 5,508 $ (7,217 ) $ (1,709 ) June 30, 2018 December 31, 2017 Net derivatives as reflected on the balance sheets (in thousands) Heating oil and coal Other current assets $ 7,867 $ 5,508 Coal Accrued expenses and other current liabilities (26,069 ) (7,217 ) $ (18,202 ) $ (1,709 ) The Company had a current asset representing cash collateral posted to a margin account for derivative positions primarily related to coal derivatives of $41.1 million and $16.2 million at June 30, 2018 and December 31, 2017 , respectively. These amounts are not included with the derivatives presented in the table above and are included in “other current assets” in the accompanying Condensed Consolidated Balance Sheets. The effects of derivatives on measures of financial performance are as follows: Derivatives used in Cash Flow Hedging Relationships (in thousands) Three Months Ended June 30, Gain (Loss) Recognized in Other Comprehensive Income (Effective Portion) Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion) 2018 2017 2018 2017 Coal sales (1) $ (15,462 ) $ 49 $ — $ — Coal purchases (2) 2,705 (34 ) — — Totals $ (12,757 ) $ 15 $ — $ — No ineffectiveness or amounts excluded from effectiveness testing relating to the Company’s cash flow hedging relationships were recognized in the results of operations in the three month periods ended June 30, 2018 and 2017 . Derivatives Not Designated as Hedging Instruments (in thousands) Three Months Ended June 30, Gain (Loss) Recognized 2018 2017 Coal trading — realized and unrealized (3) $ 384 $ (836 ) Coal risk management — unrealized (3) $ (15,505 ) $ — Natural gas trading— realized and unrealized (3) $ (17 ) $ (27 ) Change in fair value of coal derivatives and coal trading activities, net total $ (15,138 ) $ (863 ) Coal risk management— realized (4) $ (1,649 ) $ — Heating oil — diesel purchases (4) $ 3,657 $ (1,147 ) ____________________________________________________________ Location in statement of operations: (1) — Revenues (2) — Cost of sales (3) — Change in fair value of coal derivatives and coal trading activities, net (4) — Other operating (income) expense, net Derivatives used in Cash Flow Hedging Relationships (in thousands) Six Months Ended June 30, Gain (Loss) Recognized in Other Comprehensive Income (Effective Portion) Gains (Losses) Reclassified from Other Comprehensive Income into Income 2018 2017 2018 2017 Coal sales (1) $ (10,231 ) $ 269 $ — $ — Coal purchases (2) 2,163 (234 ) — — Totals $ (8,068 ) $ 35 $ — $ — No ineffectiveness or amounts excluded from effectiveness testing relating to the Company’s cash flow hedging relationships were recognized in the results of operations in the six month periods ended June 30, 2018 and 2017 . Derivatives Not Designated as Hedging Instruments (in thousands) Six Months Ended June 30, Gain (Loss) Recognized 2018 2017 Coal trading — realized and unrealized (3) $ 942 $ (1,494 ) Coal risk management — unrealized (3) $ (12,630 ) $ 26 Natural gas trading— realized and unrealized (3) $ (36 ) $ (249 ) Change in fair value of coal derivatives and coal trading activities, net total $ (11,724 ) $ (1,717 ) Coal risk management— realized (4) $ (2,680 ) $ — Heating oil — diesel purchases (4) $ 3,675 $ (4,725 ) ____________________________________________________________ Location in statement of operations: (1) — Revenues (2) — Cost of sales (3) — Change in fair value of coal derivatives and coal trading activities, net (4) — Other operating (income) expense, net Based on fair values at June 30, 2018 , amounts on derivative contracts designated as hedge instruments in cash flow hedges to be reclassified from other comprehensive income into earnings during the next twelve months are losses of approximately $7.5 million .

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	6 Months Ended
	Jun. 30, 2018
Payables and Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consist of the following: June 30, December 31, 2018 2017 (In thousands) Payroll and employee benefits $ 41,627 $ 53,149 Taxes other than income taxes 78,501 77,017 Interest 204 246 Acquired sales contracts 634 934 Workers’ compensation 19,664 18,782 Asset retirement obligations 19,840 19,840 Other 34,260 14,193 $ 194,730 $ 184,161

Debt and Financing Arrangements

Debt and Financing Arrangements	6 Months Ended
	Jun. 30, 2018
Debt Disclosure [Abstract]
Debt and Financing Arrangements	Debt and Financing Arrangements June 30, December 31, 2018 2017 (In thousands) Term loan due 2024 ($296.3 million face value) $ 295,029 $ 296,435 Other 29,280 36,514 Debt issuance costs (6,619 ) (7,032 ) 317,690 325,917 Less: current maturities of debt 12,533 15,783 Long-term debt $ 305,157 $ 310,134 Term Loan Facility On March 7, 2017, the Company entered into a senior secured term loan credit agreement (the “Credit Agreement) in an aggregate principal amount of $300 million (the “Term Loan Debt Facility) with Credit Suisse AG, Cayman Islands Branch, as administrative agent and collateral agent, and the other financial institutions from time to time party thereto (collectively, the “Lenders”). The Term Loan Debt Facility was issued at 99.50% of the face amount and will mature on March 7, 2024. The term loans provided under the Term Loan Debt Facility (the “Term Loans”) are subject to quarterly principal amortization payments in an amount equal to $750,000 . On September 25, 2017, the Company entered into the First Amendment (the “First Amendment”) to its Credit Agreement. The First Amendment reduced the interest rate on the $300 million Term Loan Debt Facility to, at the option of Arch Coal, either (i) the London interbank offered rate (“LIBOR”) plus an applicable margin of 3.25% , subject to a 1.00% LIBOR floor, or (ii) a base rate plus an applicable margin of 2.25% . The First Amendment also reset the 1.00% call premium to apply to repricing events that occur on or prior to March 26, 2018. The Term Loan Debt Facility is guaranteed by all existing and future wholly owned domestic subsidiaries of the Company (collectively, the “Subsidiary Guarantors” and, together with Arch Coal, the “Loan Parties”), subject to customary exceptions, and is secured by first priority security interests on substantially all assets of the Loan Parties, including 100% of the voting equity interests of directly owned domestic subsidiaries and 65% of the voting equity interests of directly owned foreign subsidiaries, subject to customary exceptions. The Company has the right to prepay Term Loans at any time and from time to time in whole or in part without premium or penalty, upon written notice, except that any prepayment of Term Loans that bear interest at the LIBOR Rate other than at the end of the applicable interest periods therefor shall be made with reimbursement for any funding losses and redeployment costs of the Lenders resulting therefrom. The Term Loan Debt Facility is subject to certain usual and customary mandatory prepayment events, including 100% of net cash proceeds of (i) debt issuances (other than debt permitted to be incurred under the terms of the Term Loan Debt Facility) and (ii) non-ordinary course asset sales or dispositions, subject to customary thresholds, exceptions and reinvestment rights. The Term Loan Debt Facility contains customary affirmative covenants and representations. The Term Loan Debt Facility also contains customary negative covenants, which, among other things, and subject to certain exceptions, include restrictions on (i) indebtedness, (ii) liens, (iii) liquidations, mergers, consolidations and acquisitions, (iv) disposition of assets or subsidiaries, (v) affiliate transactions, (vi) creation or ownership of certain subsidiaries, partnerships and joint ventures, (vii) continuation of or change in business, (viii) restricted payments, (ix) prepayment of subordinated and junior lien indebtedness, (x) restrictions in agreements on dividends, intercompany loans and granting liens on the collateral, (xi) loans and investments, (xii) sale and leaseback transactions, (xiii) changes in organizational documents and fiscal year and (xiv) transactions with respect to bonding subsidiaries. The Term Loan Debt Facility does not contain any financial maintenance covenant. The Term Loan Debt Facility contains customary events of default, subject to customary thresholds and exceptions, including, among other things, (i) nonpayment of principal and nonpayment of interest and fees, (ii) a material inaccuracy of a representation or warranty at the time made, (iii) a failure to comply with any covenant, subject to customary grace periods in the case of certain affirmative covenants, (iv) cross-events of default to indebtedness of at least $50 million , (v) cross-events of default to surety, reclamation or similar bonds securing obligations with an aggregate face amount of at least $50 million , (vi) uninsured judgments in excess of $50 million , (vii) any loan document shall cease to be a legal, valid and binding agreement, (viii) uninsured losses or proceedings against assets with a value in excess of $50 million , (ix) certain ERISA events, (x) a change of control or (xi) bankruptcy or insolvency proceedings relating to the Company or any material subsidiary of the Company. Second Amendment to Term Loan Facility On April 3, 2018, the Company entered into the Second Amendment (the “Second Amendment”) to its Credit Agreement. The Second Amendment further reduces the interest rate on its Term Loan Debt Facility to, at the option of Arch Coal, either (i) the London interbank offered rate (“LIBOR”) plus an applicable margin of 2.75% , subject to a 1.00% LIBOR floor, or (ii) a base rate plus an applicable margin of 1.75% . The Second Amendment also resets the 1.00% call premium to apply to repricing events that occur on or prior to October 3, 2018. The LIBOR floor remains at 1.00% . There is no change to the maturities as a result of the Second Amendment. Accounts Receivable Securitization Facility On April 27, 2017, the Company extended and amended its existing trade accounts receivable securitization facility provided to Arch Receivable Company, LLC, a special-purpose entity that is a wholly owned subsidiary of Arch Coal (“Arch Receivable”) (the “Extended Securitization Facility”), which supports the issuance of letters of credit and requests for cash advances. The amendment to the Extended Securitization Facility decreases the borrowing capacity from $200 million to $160 million and extends the maturity date to the date that is three years after the Securitization Facility Closing Date. Pursuant to the Extended Securitization Facility, Arch Receivable also agreed to a revised schedule of fees payable to the administrator and the providers of the Extended Securitization Facility. The Extended Securitization Facility will terminate at the earliest of (i) three years from the Securitization Facility Closing Date, (ii) if the Liquidity (defined in the Extended Securitization Facility and consistent with the definition in the Inventory Facility) is less than $175 million for a period of 60 consecutive days, the date that is the 364th day after the first day of such 60 consecutive day period and (iii) the occurrence of certain predefined events substantially consistent with the existing transaction documents. Under the Extended Securitization Facility, Arch Receivable, Arch Coal and certain of Arch Coal’s subsidiaries party to the Extended Securitization Facility have granted to the administrator of the Extended Securitization Facility a first priority security interest in eligible trade accounts receivable generated by such parties from the sale of coal and all proceeds thereof. As of June 30, 2018 , letters of credit totaling $75.3 million were outstanding under the facility which had a borrowing base of $79.5 million. As a result, there was no cash collateral required to be posted in the facility. Inventory-Based Revolving Credit Facility On April 27, 2017, the Company and certain subsidiaries of Arch Coal entered into a senior secured inventory-based revolving credit facility in an aggregate principal amount of $40 million (the “Inventory Facility”) with Regions Bank (“Regions”) as administrative agent and collateral agent, as lender and swingline lender (in such capacities, the “ Lender ”) and as letter of credit issuer. Availability under the Inventory Facility is subject to a borrowing base consisting of (i) 85% of the net orderly liquidation value of eligible coal inventory, (ii) the lesser of (x) 85% of the net orderly liquidation value of eligible parts and supplies inventory and (y) 35% of the amount determined pursuant to clause (i), and (iii) 100% of Arch Coal’s Eligible Cash (defined in the Inventory Facility), subject to reduction for reserves imposed by Regions. The commitments under the Inventory Facility will terminate on the date that is the earliest to occur of (i) the third anniversary of the Inventory Facility Closing Date, (ii) the date, if any, that is 364 days following the first day that Liquidity (defined in the Inventory Facility and consistent with the definition in the Extended Securitization Facility (as defined below)) is less than $250 million for a period of 60 consecutive days and (iii) the date, if any, that is 60 days following the maturity, termination or repayment in full of the Extended Securitization Facility. Revolving loan borrowings under the Inventory Facility bear interest at a per annum rate equal to, at the option of Arch Coal, either the base rate or the London interbank offered rate plus, in each case, a margin ranging from 2.25% to 2.50% (in the case of LIBOR loans) and 1.25% to 1.50% (in the case of base rate loans) determined using a Liquidity-based grid. Letters of credit under the Inventory Facility are subject to a fee in an amount equal to the applicable margin for LIBOR loans, plus customary fronting and issuance fees. All existing and future direct and indirect domestic subsidiaries of Arch Coal, subject to customary exceptions, will either constitute co-borrowers under or guarantors of the Inventory Facility (collectively with Arch Coal, the “Loan Parties”). The Inventory Facility is secured by first priority security interests in the ABL Priority Collateral (defined in the Inventory Facility) of the Loan Parties and second priority security interests in substantially all other assets of the Loan Parties, subject to customary exceptions (including an exception for the collateral that secures the Extended Securitization Facility). Arch Coal has the right to prepay borrowings under the Inventory Facility at any time and from time to time in whole or in part without premium or penalty, upon written notice, except that any prepayment of such borrowings that bear interest at the LIBOR rate other than at the end of the applicable interest periods therefore shall be made with reimbursement for any funding losses and redeployment costs of the Lender resulting therefrom. The Inventory Facility is subject to certain usual and customary mandatory prepayment events, including non-ordinary course asset sales or dispositions, subject to customary thresholds, exceptions (including exceptions for required prepayments under Arch Coal’s term loan facility) and reinvestment rights. The Inventory Facility contains certain customary affirmative and negative covenants; events of default, subject to customary thresholds and exceptions; and representations, including certain cash management and reporting requirements that are customary for asset-based credit facilities. The Inventory Facility also includes a requirement to maintain Liquidity equal to or exceeding $175 million at all times. As of June 30, 2018 , letters of credit totaling $35.2 million were outstanding under the facility with $4.8 million available for borrowings. Interest Rate Swaps During the second quarter of 2017, the Company entered into a series of interest rate swaps to fix a portion of the LIBOR interest rate within the term loan. The interest rate swaps qualify for cash flow hedge accounting treatment and as such, the change in the fair value of the interest rate swaps are recorded on the Company’s Condensed Consolidated Balance Sheet as an asset or liability with the effective portion of the gains or losses reported as a component of accumulated other comprehensive income and the ineffective portion reported in earnings. As interest payments are made on the term loan, amounts in accumulated other comprehensive income will be reclassified into earnings through interest expense to reflect a net interest on the term loan equal to the effective yield of the fixed rate of the swap plus 2.75% which is the spread on the revised LIBOR term loan. In the event that an interest rate swap is terminated prior to maturity, gains or losses in accumulated other comprehensive income will remain deferred and reclassified into earnings in the periods which the hedged forecasted transaction affects earnings. Below is a summary of the Company’s outstanding interest rate swap agreements designated as hedges as of June 30, 2018 : Notional Amount (in millions) Effective Date Fixed Rate Receive Rate Expiration Date $250.0 June 29, 2018 1.662% 1-month LIBOR June 28, 2019 $200.0 June 28, 2019 1.952% 1-month LIBOR June 30, 2020 $100.0 June 30, 2020 2.182% 1-month LIBOR June 30, 2021 The fair value of the interest rate swaps at June 30, 2018 is an asset of $4.2 million which is recorded within Other noncurrent assets with the offset to accumulated other comprehensive income on the Company’s Condensed Consolidated Balance Sheet. The Company realized $0.3 million and $0.5 million of gains during the three and six months ended June 30, 2018 , respectively, related to settlements of the interest rate swaps which was recorded to interest expense on the Company’s Condensed Consolidated Income Statements. The interest rate swaps are classified as level 2 within the fair value hierarchy. Financing Costs The Company paid $0.5 million of financing costs during the six months ended June 30, 2018 related to the Second Amendment to the Term Loan Facility discussed above. During the six months ended June 30, 2017 , the Company paid $8.9 million of financing costs primarily related to the issuance of the Term Loan Debt facility discussed above. These issuance costs were capitalized and amortized using the effective interest method over the term of the facility. The Company incurred $2.1 million of legal and financial advisory fees associated with debt refinancing activities during the six months ended June 30, 2017 related to the extinguishment of its previously existing first lien debt facility and initial efforts to replace the accounts receivable securitization facility.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes A reconciliation of the statutory federal income tax provision (benefit) at the statutory rate to the actual provision for (benefit from) income taxes follows: Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 (In thousands) Income tax provision (benefit) at statutory rate $ 8,387 $ 13,118 $ 20,870 $ 31,496 Percentage depletion allowance (2,488 ) (5,692 ) (7,095 ) (12,731 ) State taxes, net of effect of federal taxes 583 408 1,337 891 Change in valuation allowance (7,317 ) (8,316 ) (17,956 ) (20,218 ) Other, net (2,531 ) 801 (1,066 ) 1,721 Provision for (benefit from) income taxes $ (3,366 ) $ 319 $ (3,910 ) $ 1,159 The tax provision for the three and six months ended June 30, 2018 includes a $3.3 million release of a FIN 48 reserve for an Australian tax exposure due to the expiration of the local country statute. On December 22, 2017 the Tax Cut and Jobs Act of 2017 (the “Act”) was signed into law making significant changes to the Internal Revenue Code. Changes include, but are not limited to, a corporate tax rate decrease from 35% to 21% effective for tax years beginning after December 31, 2017, the elimination of the corporate alternative minimum tax regime effective for tax years beginning after December 31, 2017, implementation of a process whereby corporations with unused alternative minimum tax credits will be refunded during 2018-2022, the transition of U.S. international taxation from a worldwide tax system to a territorial system, a one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings as of December 31, 2017, further limitation on the deductibility of certain executive compensation, allowance for immediate capital expensing of certain qualified property, and limitations on the amount of interest expense deductible beginning in 2018. The Company has not completed its analysis for the income tax effects of the Act but has provided its best estimate of the impact of the Act for 2017 in its year-end income tax provision in accordance with the guidance and interpretations available at that time as provided under SAB 118. The Company has also recorded provisional adjustments under SAB 118 as part of the forecasted effective tax rate for 2018. The Company will finalize the analysis for the estimate by December 22, 2018, within the one year measurement period under SAB 118.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The hierarchy of fair value measurements assigns a level to fair value measurements based on the inputs used in the respective valuation techniques. The levels of the hierarchy, as defined below, give the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs. · Level 1 is defined as observable inputs such as quoted prices in active markets for identical assets. Level 1 assets include U.S. Treasury securities, and coal swaps and futures that are submitted for clearing on the New York Mercantile Exchange. · Level 2 is defined as observable inputs other than Level 1 prices. These include quoted prices for similar assets or liabilities in an active market, quoted prices for identical assets and liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. The Company’s level 2 assets and liabilities include U.S. government agency securities, coal commodity contracts and interest rate swaps with fair values derived from quoted prices in over-the-counter markets or from prices received from direct broker quotes. · Level 3 is defined as unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions. These include the Company’s commodity option contracts (coal, natural gas and heating oil) valued using modeling techniques, such as Black-Scholes, that require the use of inputs, particularly volatility, that are rarely observable. Changes in the unobservable inputs would not have a significant impact on the reported Level 3 fair values at June 30, 2018 . The table below sets forth, by level, the Company’s financial assets and liabilities that are recorded at fair value in the accompanying Condensed Consolidated Balance Sheet: June 30, 2018 Total Level 1 Level 2 Level 3 (In thousands) Assets: Investments in marketable securities $ 160,894 $ 54,832 $ 106,062 $ — Derivatives 12,031 593 4,786 6,652 Total assets $ 172,925 $ 55,425 $ 110,848 $ 6,652 Liabilities: Derivatives $ 26,069 $ 24,862 $ 638 $ 569 The Company’s contracts with its counterparties allow for the settlement of contracts in an asset position with contracts in a liability position in the event of default or termination. For classification purposes, the Company records the net fair value of all the positions with these counterparties as a net asset or liability. Each level in the table above displays the underlying contracts according to their classification in the accompanying Condensed Consolidated Balance Sheet, based on this counterparty netting. The following table summarizes the change in the fair values of financial instruments categorized as Level 3. Three Months Ended June 30, 2018 Six Months Ended June 30, 2018 (In thousands) Balance, beginning of period $ 4,969 $ 5,426 Realized and unrealized gains recognized in earnings, net 3,628 3,653 Purchases 823 1,656 Issuances (580 ) (654 ) Settlements (2,757 ) (3,998 ) Ending balance $ 6,083 $ 6,083 Net unrealized gains of $1.5 million and $3.0 million were recognized in the Condensed Consolidated Income Statements within Other operating income, net during the three and six months ended June 30, 2018 , respectively, related to Level 3 financial instruments held on June 30, 2018 . Fair Value of Long-Term Debt At June 30, 2018 and December 31, 2017 , the fair value of the Company’s debt, including amounts classified as current, was $327.1 million and $336.1 million , respectively. Fair values are based upon observed prices in an active market, when available, or from valuation models using market information, which fall into Level 2 in the fair value hierarchy.

Earnings per Common Share

Earnings per Common Share	6 Months Ended
	Jun. 30, 2018
Earnings Per Share [Abstract]
Earnings per Common Share	Earnings per Common Share The Company computes basic net income per share using the weighted average number of common shares outstanding during the period. Diluted net income per share is computed using the weighted average number of common shares and the effect of potentially dilutive securities outstanding during the period. Potentially dilutive securities may consist of warrants, restricted stock units or other contingently issuable shares. The dilutive effect of outstanding warrants, restricted stock units and other contingently issuable shares is reflected in diluted earnings per share by application of the treasury stock method. The following table provides the basis for basic and diluted earnings per share by reconciling the denominators of the computations: Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 (In thousands) Weighted average shares outstanding: Basic weighted average shares outstanding 20,156 24,659 20,529 24,834 Effect of dilutive securities 880 423 927 411 Diluted weighted average shares outstanding 21,036 25,082 21,456 25,245

Workers Compensation Expense

Workers Compensation Expense	6 Months Ended
	Jun. 30, 2018
Compensation Related Costs [Abstract]
Workers Compensation Expense	Workers Compensation Expense The Company is liable under the Federal Mine Safety and Health Act of 1969, as subsequently amended, to provide for pneumoconiosis (occupational disease) benefits to eligible employees, former employees and dependents. The Company currently provides for federal claims principally through a self-insurance program. The Company is also liable under various state workers’ compensation statutes for occupational disease benefits. The occupational disease benefit obligation represents the present value of the actuarially computed present and future liabilities for such benefits over the employees’ applicable years of service. In addition, the Company is liable for workers’ compensation benefits for traumatic injuries which are calculated using actuarially-based loss rates, loss development factors and discounted based on a risk free rate. Traumatic workers’ compensation claims are insured with varying retentions/deductibles, or through state-sponsored workers’ compensation programs. Workers’ compensation expense consists of the following components: Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 (In thousands) Self-insured occupational disease benefits: Service cost $ 1,860 $ 1,559 $ 3,720 $ 3,117 Interest cost (1) 1,194 1,168 2,389 2,337 Total occupational disease $ 3,054 $ 2,727 $ 6,109 $ 5,454 Traumatic injury claims and assessments 2,188 2,532 5,199 5,410 Total workers’ compensation expense $ 5,242 $ 5,259 $ 11,308 $ 10,864 (1) In accordance with the adoption of ASU 2017-07, “Compensation-Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost,” these costs are recorded within Nonoperating expenses in the Condensed Consolidated Income Statements on the line item “Non-service related pension and postretirement benefit costs.” For additional information about the adoption of the standard, see Note 2 , “ Accounting Policies ” in the Condensed Consolidated Financial Statements.

Employee Benefit Plans

Employee Benefit Plans	6 Months Ended
	Jun. 30, 2018
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Employee Benefit Plans	Employee Benefit Plans The following table details the components of pension benefit costs (credits): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 (In thousands) Interest cost (1) $ 2,270 $ 2,991 $ 4,541 $ 5,982 Expected return on plan assets (1) (3,080 ) (4,499 ) (6,161 ) (8,996 ) Pension settlement (1) (1,371 ) (487 ) (1,371 ) (487 ) Net benefit credit $ (2,181 ) $ (1,995 ) $ (2,991 ) $ (3,501 ) During the second quarter of 2018, the Company recorded a pension settlement related to its cash balance pension plan as the qualifying distributions from the plan exceeded the annual service and interest costs of the plan. Additionally, in accordance with accounting guidance, the Company revalued the cash balance pension plan liability which reduced the liability by approximately $5.0 million with the offset to accumulated other comprehensive income. The discount rate used for the revaluation was 4.11% . The following table details the components of other postretirement benefit costs: Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 (In thousands) Service cost $ 139 $ 171 $ 279 $ 341 Interest cost (1) 919 1,059 1,837 2,117 Net benefit cost $ 1,058 $ 1,230 $ 2,116 $ 2,458 (1) In accordance with the adoption of ASU 2017-07, “Compensation-Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost,” these costs are recorded within Nonoperating expenses in the Condensed Consolidated Income Statements on the line item “Non-service related pension and postretirement benefit costs.” For additional information about the adoption of the standard, see Note 2 , “ Accounting Policies ” in the Condensed Consolidated Financial Statements.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies The Company accrues for costs related to contingencies when a loss is probable and the amount is reasonably determinable. Disclosure of contingencies is included in the financial statements when it is at least reasonably possible that a material loss or an additional material loss in excess of amounts already accrued may be incurred. In addition, the Company is a party to numerous other claims and lawsuits with respect to various matters. As of June 30, 2018 and December 31, 2017 , the Company had accrued $0.4 million and $0.2 million , respectively, for all legal matters, of which all amounts are classified as current. The ultimate resolution of any such legal matter could result in outcomes which may be materially different from amounts the Company has accrued for such matters.

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 2018
Segment Reporting [Abstract]
Segment Information	Segment Information The Company’s reportable business segments are based on two distinct lines of business, metallurgical and thermal, and may include a number of mine complexes. The Company manages its coal sales by market, not by individual mining complex. Geology, coal transportation routes to customers, and regulatory environments also have a significant impact on the Company’s marketing and operations management. Mining operations are evaluated based on Adjusted EBITDA, per-ton cash operating costs (defined as including all mining costs except depreciation, depletion, amortization, accretion on asset retirement obligations, and pass-through transportation expenses), and on other non-financial measures, such as safety and environmental performance. Adjusted EBITDA is not a measure of financial performance in accordance with generally accepted accounting principles, and items excluded from Adjusted EBITDA are significant in understanding and assessing our financial condition. Therefore, Adjusted EBITDA should not be considered in isolation, nor as an alternative to net income, income from operations, cash flows from operations or as a measure of our profitability, liquidity or performance under generally accepted accounting principles. The Company uses Adjusted EBITDA to measure the operating performance of its segments and allocate resources to the segments. Furthermore, analogous measures are used by industry analysts and investors to evaluate the Company’s operating performance. Investors should be aware that the Company’s presentation of Adjusted EBITDA may not be comparable to similarly titled measures used by other companies. The Company reports its results of operations primarily through the following reportable segments: Powder River Basin (PRB) segment containing the Company’s primary thermal operations in Wyoming; the Metallurgical (MET) segment, containing the Company’s metallurgical operations in West Virginia, Kentucky, and Virginia, and the Other Thermal segment containing the Company’s supplementary thermal operations in Colorado, Illinois, and West Virginia. Periods presented in this note have been recast for comparability. On September 14, 2017, the Company closed on its’ definitive agreement to sell Lone Mountain Processing LLC, an operating mine complex within the Company’s metallurgical coal segment. Through this transaction the Company divested all active operations in the states of Kentucky and Virginia. Operating segment results for the three and six months ended June 30, 2018 and 2017 , are presented below. The Company measures its segments based on “adjusted earnings before interest, taxes, depreciation, depletion, amortization, accretion on asset retirements obligations, and nonoperating expenses (Adjusted EBITDA).” Adjusted EBITDA does not reflect mine closure or impairment costs, since those are not reflected in the operating income reviewed by management. The Corporate, Other and Eliminations grouping includes these charges, as well as the change in fair value of coal derivatives and coal trading activities, net; corporate overhead; land management activities; other support functions; and the elimination of intercompany transactions. PRB MET Other Thermal Corporate, Other and Eliminations Consolidated (in thousands) Three Months Ended June 30, 2018 Revenues $ 229,878 $ 259,032 $ 99,814 $ 3,625 $ 592,349 Adjusted EBITDA 26,491 86,657 11,842 (39,605 ) 85,385 Depreciation, depletion and amortization 8,304 18,018 3,701 526 30,549 Accretion on asset retirement obligation 4,885 469 565 1,074 6,993 Total assets 379,613 551,012 134,319 884,469 1,949,413 Capital expenditures 3,065 11,899 2,559 3,073 20,596 Three Months Ended June 30, 2017 Revenues $ 230,579 $ 227,649 $ 91,639 $ (1 ) $ 549,866 Adjusted EBITDA 31,789 62,552 26,910 (25,651 ) 95,600 Depreciation, depletion and amortization 8,574 18,385 3,285 457 30,701 Accretion on asset retirement obligation 5,040 528 540 1,515 7,623 Total assets 426,793 580,543 126,870 997,852 2,132,058 Capital expenditures 822 6,825 1,899 1,426 10,972 Six Months Ended June 30, 2018 Revenues $ 475,306 $ 497,379 $ 191,334 $ 3,625 $ 1,167,644 Adjusted EBITDA 53,993 170,399 27,510 (61,604 ) 190,298 Depreciation, depletion and amortization 16,727 35,003 7,536 986 60,252 Accretion on asset retirement obligation 9,771 937 1,130 2,147 13,985 Total assets 379,613 551,012 134,319 884,469 1,949,413 Capital expenditures 3,763 17,728 3,765 4,793 30,049 Six Months Ended June 30, 2017 Revenues $ 504,007 $ 453,232 $ 193,545 $ 57 $ 1,150,841 Adjusted EBITDA 79,794 130,862 54,152 (47,989 ) 216,819 Depreciation, depletion and amortization 18,085 37,149 6,485 903 62,622 Accretion on asset retirement obligation 10,080 1,057 1,080 3,029 15,246 Total assets 426,793 580,543 126,870 997,852 2,132,058 Capital expenditures 950 11,436 2,640 1,896 16,922 A reconciliation of net income to adjusted EBITDA follows: Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 (In thousands) Net income $ 43,306 $ 37,160 $ 103,291 $ 88,828 Provision for (benefit from) income taxes $ (3,366 ) $ 319 $ (3,910 ) $ 1,159 Interest expense, net 3,498 5,161 7,620 14,059 Depreciation, depletion and amortization 30,549 30,701 60,252 62,622 Accretion on asset retirement obligations 6,993 7,623 13,985 15,246 Amortization of sales contracts, net 3,248 14,352 6,299 29,042 Net loss resulting from early retirement of debt and debt restructuring 485 31 485 2,061 Non-service related pension and postretirement benefit costs (68 ) 232 1,235 953 Reorganization items, net 740 21 1,041 2,849 Adjusted EBITDA $ 85,385 $ 95,600 $ 190,298 $ 216,819

Revenue Recognition

Revenue Recognition	6 Months Ended
	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Revenue Recognition	Revenue Recognition ASC 606-10-50-5 requires that entities disclose disaggregated revenue information in categories (such as type of good or service, geography, market, type of contract, etc.) that depict how the nature, amount, timing, and uncertainty of revenue and cash flow are affected by economic factors. ASC 606-10-55-89 explains that the extent to which an entity’s revenue is disaggregated depends on the facts and circumstances that pertain to the entity’s contracts with customers and that some entities may need to use more than one type of category to meet the objective for disaggregating revenue. In general, the Company’s business segmentation is aligned according to the nature and economic characteristics of its coal and customer relationships and provides meaningful disaggregation of each segment’s results. The company has further disaggregated revenue between North America and Seaborne revenues which depicts the pricing and contract differences between the two. North America revenue is characterized by contracts with a term of one year or longer and typically the pricing is fixed; whereas Seaborne revenue generally is derived by spot or short term contracts with an indexed based pricing mechanism. PRB MET Other Thermal Corporate, Other and Eliminations Consolidated (in thousands) Three Months Ended June 30, 2018 North America revenues $ 229,035 $ 38,323 $ 40,547 $ 3,625 $ 311,530 Seaborne revenues 843 220,709 59,267 — 280,819 Total revenues $ 229,878 $ 259,032 $ 99,814 $ 3,625 $ 592,349 Three Months Ended June 30, 2017 North America revenues $ 230,579 $ 82,498 $ 71,539 $ (1 ) $ 384,615 Seaborne revenues — 145,151 20,100 — 165,251 Total revenues $ 230,579 $ 227,649 $ 91,639 $ (1 ) $ 549,866 PRB MET Other Thermal Corporate, Other and Eliminations Consolidated (in thousands) Six Months Ended June 30, 2018 North America revenues $ 473,395 $ 68,001 $ 84,214 $ 3,625 $ 629,235 Seaborne revenues 1,911 429,378 107,120 — 538,409 Total revenues $ 475,306 $ 497,379 $ 191,334 $ 3,625 $ 1,167,644 Six Months Ended June 30, 2017 North America revenues $ 504,007 $ 151,233 $ 140,503 $ 57 $ 795,800 Seaborne revenues — 301,999 53,042 — 355,041 Total revenues $ 504,007 $ 453,232 $ 193,545 $ 57 $ 1,150,841 As of June 30, 2018 , the Company has outstanding performance obligations for the remainder of 2018 of 35.0 million tons of fixed price contracts and 4.9 million tons of variable price contracts. Additionally, the Company has outstanding performance obligations beyond 2018 of approximately 70.8 million tons of fixed price contracts and 6.4 million tons of variable price contracts.

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On July 26, 2018, the board of directors of Arch Coal authorized an incremental $250 million increase to the share repurchase program bringing the total authorization to $750 million . The timing of any future share purchases, and the ultimate number of shares to be purchased, will depend on a number of factors, including business and market conditions, our future financial performance, and other capital priorities. The shares will be acquired in the open market or through private transactions in accordance with Securities and Exchange Commission requirements. As of June 30, 2018 , we had repurchased 5,344,411 shares at an average share price of $78.40 per share for an aggregate purchase price of approximately $419 million since inception of the stock repurchase program. The Company had 19,587,748 common shares outstanding as of July 27, 2018 . The purchases under the share repurchase program may be made in the open market or through privately negotiated transactions from time to time and in accordance with applicable laws, rules and regulations. Repurchases may also be made pursuant to a Rule 10b5-1 plan, which permits shares to be repurchased in accordance with pre-determined criteria when the Company might otherwise be prohibited from doing so under insider trading laws or because of self-imposed trading blackout periods. The share repurchase program may be amended, suspended or discontinued at any time and does not commit the Company to repurchase shares of its common stock. The actual number and value of the shares to be purchased will depend on the performance of the Company’s stock price and other market conditions.

Basis of Presentation (Policies

Basis of Presentation (Policies)	6 Months Ended
	Jun. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States for interim financial reporting and U.S. Securities and Exchange Commission regulations. In the opinion of management, all adjustments, consisting of normal, recurring accruals considered necessary for a fair presentation, have been included. Results of operations for the three and six months ended June 30, 2018 are not necessarily indicative of results to be expected for the year ending December 31, 2018 . These financial statements should be read in conjunction with the audited financial statements and related notes as of and for the year ended December 31, 2017 included in the Company’s Annual Report on Form 10-K filed with the U.S. Securities and Exchange Commission.
Recently Adopted Accounting Guidance and Recent Accounting Guidance Issued Not Yet Effective	In March 2017, the FASB issued ASU 2017-07, “Compensation-Retirement Benefits (Topic 715) Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost.” ASU 2017-07 changes the income statement presentation of defined benefit plan expense by requiring separation between operating expense (service cost component) and non-operating expense (all other components, including interest cost, amortization of prior service cost, curtailments and settlements, etc.). The operating expense component is reported with similar compensation costs while the non-operating components are reported in Nonoperating expense. In addition, only the service cost component is eligible for capitalization as part of an asset such as inventory or property, plant and equipment. The ASU is effective for public companies for fiscal years beginning after December 15, 2017, and interim periods therein. The ASU should be adopted using a retrospective transition method to each period presented. The Company adopted ASU 2017-07 effective January 1, 2018 and applied the ASU retrospectively to the periods presented in the Company's Condensed Consolidated Income Statements. The retrospective application resulted in a $0.6 million and $1.5 million reduction in cost of coal sales and a $0.3 million and $0.5 million increase in selling, general and administrative costs with the corresponding offset to Nonoperating expense for the three and six months ended June 30, 2017 . Recent Accounting Guidance Issued Not Yet Effective In February 2016, the FASB issued ASU 2016-02, “Leases” which, for operating leases, requires a lessee to recognize a right-of-use asset and a lease liability, initially measured at the present value of the lease payments, in its balance sheet. The standard also requires a lessee to recognize a single lease cost, calculated so that the cost of the lease is allocated over the term of the lease, on a generally straight line basis. The ASU is effective for public companies for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years; early adoption is permitted. The Company has both operating and capital leases. We expect the adoption of this standard to result in the recognition of right-of-use assets and lease liabilities not currently recorded on the Company’s financial statements. The Company is currently in the process of accumulating all contractual lease arrangements in order to determine the impact on its financial statements. 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 anticipates early adopting the standard in the third quarter of 2018, although we do not expect a significant impact to the Company’s financial results. In February 2018, the FASB issued ASU 2018-02, “Income Statement-Reporting Comprehensive Income (Topic 220) Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.” ASU 2018-02 provides an option to reclassify stranded tax effects within accumulated other comprehensive income to retained earnings due to the change in the U.S. federal tax rate in the Tax Cuts and Jobs Act of 2017. The ASU is effective for public companies for fiscal years beginning after December 15, 2018, and interim periods therein with early adoption permitted. The Company is currently in the process of analyzing the standard, but does not expect a significant impact to the Company’s financial statements. Recently Adopted Accounting Guidance In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers.” ASU 2014-09 is a comprehensive revenue recognition standard that has superseded nearly all existing revenue recognition guidance under current U.S. GAAP and replaced it with a principle based approach for determining revenue recognition. ASU 2014-09 requires that companies recognize revenue based on the value of transferred goods or services as they occur in the contract. The ASU also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. ASU 2014-09 is effective for interim and annual periods beginning after December 15, 2017. The Company’s primary source of revenue is from the sale of coal through both short-term and long-term contracts with utilities, industrial customers and steel producers whereby revenue is currently recognized when risk of loss has passed to the customer. During the fourth quarter of 2017, the Company finalized its assessment related to the new standard by analyzing certain contracts representative of the majority of the Company’s coal sales and determined that the timing of revenue recognition related to the Company’s coal sales will remain consistent between the new standard and the previous standard. The Company also reviewed other sources of revenue, and concluded the current basis of accounting for these items is in accordance with the new standard. The Company adopted ASU 2014-09 effective January 1, 2018 using the modified retrospective method, and there was no cumulative adjustment to retained earnings. The Company also reviewed the disclosure requirements under the new standard and has compiled information needed for the expanded disclosures which are included within Note 18 , “ Revenue Recognition ” in the Condensed Consolidated Financial Statements. In August 2016, the FASB issued ASU 2016-15, “Classification of Certain Cash Receipts and Cash Payments.” The amendment requires the classification of certain cash receipts and cash payments in the statement of cash flows to reduce diversity in practice. The new guidance is effective for fiscal years beginning after December 15, 2017 and the interim periods therein, with early adoption permitted. The amendments in the classification should be applied retrospectively to all periods presented, unless deemed impracticable, in which case, the prospective application is permitted. The Company adopted ASU 2016-15 effective January 1, 2018 with no impact on the Company’s financial statements. In November 2016, FASB issued ASU 2016-18, “Statement of Cash Flows (Topic 230): Restricted Cash.” The ASU applies to all entities that have restricted cash or restricted cash equivalents and are required to present a statement of cash flows. The ASU requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. As a result, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning of period and end of period total amounts shown on the statement of cash flows. The ASU is effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. The ASU should be adopted using a retrospective transition method to each period presented. The Company adopted ASU 2016-18 effective January 1, 2018 and applied the ASU retrospectively to the periods presented in the Company's Condensed Consolidated Statements of Cash Flow.

Accounting Policies (Tables)

Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Schedule of net cash used in investing activities	As a result, net cash used in investing activities for the six months ended June 30, 2017 was adjusted to exclude the change in restricted cash as follows: (in thousands) Six Months Ended June 30, 2017 Cash used in investing activities previously reported $ (68,915 ) Less: Withdrawals of restricted cash 29,295 Cash used in investing activities $ (98,210 )

Accumulated Other Comprehensi28

Accumulated Other Comprehensive Income (Tables)	6 Months Ended
	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The following items are included in accumulated other comprehensive income ("AOCI"): Pension, Postretirement and Other Accumulated Post- Other Derivative Employment Available-for- Comprehensive Instruments Benefits Sale Securities Income (In thousands) Balance at December 31, 2017 $ 647 $ 19,720 $ — $ 20,367 Unrealized gains (losses) (5,248 ) 5,024 (465 ) (689 ) Amounts reclassified from AOCI (488 ) (1,371 ) (16 ) (1,875 ) Balance at June 30, 2018 $ (5,089 ) $ 23,373 $ (481 ) $ 17,803
Schedule of Comprehensive Income Reclassifications	The following amounts were reclassified out of AOCI: Three Months Ended June 30, Six Months Ended June 30, Details About AOCI Components 2018 2017 2018 2017 Line Item in the Condensed Consolidated Statement of Operations (In thousands) Coal hedges $ — $ — $ — $ — Revenues Interest rate hedges 348 — 488 — Interest expense — — — — Provision for (benefit from) income taxes $ 348 $ — $ 488 $ — Net of tax Pension, postretirement and other post-employment benefits Pension settlement 1,371 487 1,371 487 Non-service related pension and postretirement benefit (costs) credits 1,371 487 1,371 487 — — — — Provision for (benefit from) income taxes $ 1,371 $ 487 $ 1,371 $ 487 Net of tax Available-for-sale securities $ 16 $ — $ 16 $ 332 Interest and investment income — — — — Provision for (benefit from) income taxes $ 16 $ — $ 16 $ 332 Net of tax

Inventories (Tables)

Inventories (Tables)	6 Months Ended
	Jun. 30, 2018
Inventory Disclosure [Abstract]
Inventories	Inventories consist of the following: June 30, December 31, 2018 2017 (In thousands) Coal $ 72,268 $ 54,692 Repair parts and supplies 84,937 74,268 $ 157,205 $ 128,960

Investments in Available-for-30

Investments in Available-for-Sale Securities (Tables)	6 Months Ended
	Jun. 30, 2018
Debt Securities, Available-for-sale [Abstract]
Available-for-sale Securities	The Company’s investments in available-for-sale marketable securities are as follows: June 30, 2018 Balance Sheet Classification Gross Unrealized Fair Short-Term Other Cost Basis Gains Losses Value Investments Assets (In thousands) Available-for-sale: U.S. government and agency securities $ 88,858 $ 3 $ (161 ) $ 88,700 $ 88,700 $ — Corporate notes and bonds 72,516 3 (325 ) 72,194 72,194 — Total Investments $ 161,374 $ 6 $ (486 ) $ 160,894 $ 160,894 $ — December 31, 2017 Balance Sheet Classification Gross Unrealized Fair Short-Term Other Cost Basis Gains Losses Value Investments Assets (In thousands) Available-for-sale: U.S. government and agency securities $ 64,151 $ 22 $ (73 ) $ 64,100 $ 64,100 $ — Corporate notes and bonds 92,038 — (292 ) 91,746 91,746 — Total Investments $ 156,189 $ 22 $ (365 ) $ 155,846 $ 155,846 $ —

Sales Contracts (Tables)

Sales Contracts (Tables)	6 Months Ended
	Jun. 30, 2018
Acquired Sales Contracts [Abstract]
Schedule of Sales Contracts	The sales contracts reflected in the Condensed Consolidated Balance Sheets are as follows: June 30, 2018 December 31, 2017 Assets Liabilities Net Total Assets Liabilities Net Total (In thousands) (In thousands) Original fair value $ 97,196 $ 31,742 $ 97,196 $ 31,742 Accumulated amortization (91,650 ) (30,570 ) (84,760 ) (29,979 ) Total $ 5,546 $ 1,172 $ 4,374 $ 12,436 $ 1,763 $ 10,673 Balance Sheet classification: Other current $ 5,544 $ 634 $ 12,432 $ 934 Other noncurrent $ 2 $ 538 $ 4 $ 829

Derivatives (Tables)

Derivatives (Tables)	6 Months Ended
	Jun. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Price Risk Derivatives	At June 30, 2018 , the Company held derivatives for risk management purposes that are expected to settle in the following years: (Tons in thousands) 2018 2019 Total Coal sales 1,089 1,587 2,676 Coal purchases 433 79 512
Disclosure of Fair Value of Derivatives	The fair value and location of derivatives reflected in the accompanying Condensed Consolidated Balance Sheets are as follows: June 30, 2018 December 31, 2017 Fair Value of Derivatives Asset Liability Asset Liability (In thousands) Derivative Derivative Derivative Derivative Derivatives Designated as Hedging Instruments Coal $ 1,763 $ (9,388 ) $ 942 $ (2,146 ) Derivatives Not Designated as Hedging Instruments Heating oil -- diesel purchases 6,652 — 5,354 — Coal -- held for trading purposes 35,894 (36,323 ) 44,088 (45,221 ) Coal -- risk management 6,058 (22,900 ) 5,139 (9,892 ) Natural gas 42 — 27 — Total 48,646 (59,223 ) 54,608 (55,113 ) Total derivatives 50,409 (68,611 ) 55,550 (57,259 ) Effect of counterparty netting (42,542 ) 42,542 (50,042 ) 50,042 Net derivatives as classified in the balance sheets $ 7,867 $ (26,069 ) $ (18,202 ) $ 5,508 $ (7,217 ) $ (1,709 ) June 30, 2018 December 31, 2017 Net derivatives as reflected on the balance sheets (in thousands) Heating oil and coal Other current assets $ 7,867 $ 5,508 Coal Accrued expenses and other current liabilities (26,069 ) (7,217 ) $ (18,202 ) $ (1,709 )
Effects of Derivatives on Measures of Financial Performance	Derivatives Not Designated as Hedging Instruments (in thousands) Six Months Ended June 30, Gain (Loss) Recognized 2018 2017 Coal trading — realized and unrealized (3) $ 942 $ (1,494 ) Coal risk management — unrealized (3) $ (12,630 ) $ 26 Natural gas trading— realized and unrealized (3) $ (36 ) $ (249 ) Change in fair value of coal derivatives and coal trading activities, net total $ (11,724 ) $ (1,717 ) Coal risk management— realized (4) $ (2,680 ) $ — Heating oil — diesel purchases (4) $ 3,675 $ (4,725 ) ____________________________________________________________ Location in statement of operations: (1) — Revenues (2) — Cost of sales (3) — Change in fair value of coal derivatives and coal trading activities, net (4) — Other operating (income) expense, net Derivatives Not Designated as Hedging Instruments (in thousands) Three Months Ended June 30, Gain (Loss) Recognized 2018 2017 Coal trading — realized and unrealized (3) $ 384 $ (836 ) Coal risk management — unrealized (3) $ (15,505 ) $ — Natural gas trading— realized and unrealized (3) $ (17 ) $ (27 ) Change in fair value of coal derivatives and coal trading activities, net total $ (15,138 ) $ (863 ) Coal risk management— realized (4) $ (1,649 ) $ — Heating oil — diesel purchases (4) $ 3,657 $ (1,147 ) ____________________________________________________________ Location in statement of operations: (1) — Revenues (2) — Cost of sales (3) — Change in fair value of coal derivatives and coal trading activities, net (4) — Other operating (income) expense, net Derivatives used in Cash Flow Hedging Relationships (in thousands) Six Months Ended June 30, Gain (Loss) Recognized in Other Comprehensive Income (Effective Portion) Gains (Losses) Reclassified from Other Comprehensive Income into Income 2018 2017 2018 2017 Coal sales (1) $ (10,231 ) $ 269 $ — $ — Coal purchases (2) 2,163 (234 ) — — Totals $ (8,068 ) $ 35 $ — $ — The effects of derivatives on measures of financial performance are as follows: Derivatives used in Cash Flow Hedging Relationships (in thousands) Three Months Ended June 30, Gain (Loss) Recognized in Other Comprehensive Income (Effective Portion) Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion) 2018 2017 2018 2017 Coal sales (1) $ (15,462 ) $ 49 $ — $ — Coal purchases (2) 2,705 (34 ) — — Totals $ (12,757 ) $ 15 $ — $ —

Accrued Expenses and Other Cu33

Accrued Expenses and Other Current Liabilities (Tables)	6 Months Ended
	Jun. 30, 2018
Payables and Accruals [Abstract]
Schedule of Accrued Liabilities	Accrued expenses and other current liabilities consist of the following: June 30, December 31, 2018 2017 (In thousands) Payroll and employee benefits $ 41,627 $ 53,149 Taxes other than income taxes 78,501 77,017 Interest 204 246 Acquired sales contracts 634 934 Workers’ compensation 19,664 18,782 Asset retirement obligations 19,840 19,840 Other 34,260 14,193 $ 194,730 $ 184,161

Debt and Financing Arrangemen34

Debt and Financing Arrangements (Tables)	6 Months Ended
	Jun. 30, 2018
Debt Disclosure [Abstract]
Debt	June 30, December 31, 2018 2017 (In thousands) Term loan due 2024 ($296.3 million face value) $ 295,029 $ 296,435 Other 29,280 36,514 Debt issuance costs (6,619 ) (7,032 ) 317,690 325,917 Less: current maturities of debt 12,533 15,783 Long-term debt $ 305,157 $ 310,134
Schedule of Interest Rate Derivatives	Below is a summary of the Company’s outstanding interest rate swap agreements designated as hedges as of June 30, 2018 : Notional Amount (in millions) Effective Date Fixed Rate Receive Rate Expiration Date $250.0 June 29, 2018 1.662% 1-month LIBOR June 28, 2019 $200.0 June 28, 2019 1.952% 1-month LIBOR June 30, 2020 $100.0 June 30, 2020 2.182% 1-month LIBOR June 30, 2021

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	A reconciliation of the statutory federal income tax provision (benefit) at the statutory rate to the actual provision for (benefit from) income taxes follows: Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 (In thousands) Income tax provision (benefit) at statutory rate $ 8,387 $ 13,118 $ 20,870 $ 31,496 Percentage depletion allowance (2,488 ) (5,692 ) (7,095 ) (12,731 ) State taxes, net of effect of federal taxes 583 408 1,337 891 Change in valuation allowance (7,317 ) (8,316 ) (17,956 ) (20,218 ) Other, net (2,531 ) 801 (1,066 ) 1,721 Provision for (benefit from) income taxes $ (3,366 ) $ 319 $ (3,910 ) $ 1,159

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Accounted for at Fair Value	The table below sets forth, by level, the Company’s financial assets and liabilities that are recorded at fair value in the accompanying Condensed Consolidated Balance Sheet: June 30, 2018 Total Level 1 Level 2 Level 3 (In thousands) Assets: Investments in marketable securities $ 160,894 $ 54,832 $ 106,062 $ — Derivatives 12,031 593 4,786 6,652 Total assets $ 172,925 $ 55,425 $ 110,848 $ 6,652 Liabilities: Derivatives $ 26,069 $ 24,862 $ 638 $ 569
Summary of Change in the Fair Values of Financial Instruments Categorized as Level 3	The following table summarizes the change in the fair values of financial instruments categorized as Level 3. Three Months Ended June 30, 2018 Six Months Ended June 30, 2018 (In thousands) Balance, beginning of period $ 4,969 $ 5,426 Realized and unrealized gains recognized in earnings, net 3,628 3,653 Purchases 823 1,656 Issuances (580 ) (654 ) Settlements (2,757 ) (3,998 ) Ending balance $ 6,083 $ 6,083

Earnings per Common Share (Tabl

Earnings per Common Share (Tables)	6 Months Ended
	Jun. 30, 2018
Earnings Per Share [Abstract]
Schedule of Weighted Average Number of Shares	The following table provides the basis for basic and diluted earnings per share by reconciling the denominators of the computations: Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 (In thousands) Weighted average shares outstanding: Basic weighted average shares outstanding 20,156 24,659 20,529 24,834 Effect of dilutive securities 880 423 927 411 Diluted weighted average shares outstanding 21,036 25,082 21,456 25,245

Workers Compensation Expense (T

Workers Compensation Expense (Tables)	6 Months Ended
	Jun. 30, 2018
Compensation Related Costs [Abstract]
Workers' compensation expense	Workers’ compensation expense consists of the following components: Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 (In thousands) Self-insured occupational disease benefits: Service cost $ 1,860 $ 1,559 $ 3,720 $ 3,117 Interest cost (1) 1,194 1,168 2,389 2,337 Total occupational disease $ 3,054 $ 2,727 $ 6,109 $ 5,454 Traumatic injury claims and assessments 2,188 2,532 5,199 5,410 Total workers’ compensation expense $ 5,242 $ 5,259 $ 11,308 $ 10,864 (1) In accordance with the adoption of ASU 2017-07, “Compensation-Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost,” these costs are recorded within Nonoperating expenses in the Condensed Consolidated Income Statements on the line item “Non-service related pension and postretirement benefit costs.” For additional information about the adoption of the standard, see Note 2 , “ Accounting Policies ” in the Condensed Consolidated Financial Statements.

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	6 Months Ended
	Jun. 30, 2018
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Pension Benefit Costs	The following table details the components of other postretirement benefit costs: Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 (In thousands) Service cost $ 139 $ 171 $ 279 $ 341 Interest cost (1) 919 1,059 1,837 2,117 Net benefit cost $ 1,058 $ 1,230 $ 2,116 $ 2,458 (1) In accordance with the adoption of ASU 2017-07, “Compensation-Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost,” these costs are recorded within Nonoperating expenses in the Condensed Consolidated Income Statements on the line item “Non-service related pension and postretirement benefit costs.” For additional information about the adoption of the standard, see Note 2 , “ Accounting Policies ” in the Condensed Consolidated Financial Statements. The following table details the components of pension benefit costs (credits): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 (In thousands) Interest cost (1) $ 2,270 $ 2,991 $ 4,541 $ 5,982 Expected return on plan assets (1) (3,080 ) (4,499 ) (6,161 ) (8,996 ) Pension settlement (1) (1,371 ) (487 ) (1,371 ) (487 ) Net benefit credit $ (2,181 ) $ (1,995 ) $ (2,991 ) $ (3,501 )

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 2018
Segment Reporting [Abstract]
Schedule of Operating Segment Results	PRB MET Other Thermal Corporate, Other and Eliminations Consolidated (in thousands) Three Months Ended June 30, 2018 Revenues $ 229,878 $ 259,032 $ 99,814 $ 3,625 $ 592,349 Adjusted EBITDA 26,491 86,657 11,842 (39,605 ) 85,385 Depreciation, depletion and amortization 8,304 18,018 3,701 526 30,549 Accretion on asset retirement obligation 4,885 469 565 1,074 6,993 Total assets 379,613 551,012 134,319 884,469 1,949,413 Capital expenditures 3,065 11,899 2,559 3,073 20,596 Three Months Ended June 30, 2017 Revenues $ 230,579 $ 227,649 $ 91,639 $ (1 ) $ 549,866 Adjusted EBITDA 31,789 62,552 26,910 (25,651 ) 95,600 Depreciation, depletion and amortization 8,574 18,385 3,285 457 30,701 Accretion on asset retirement obligation 5,040 528 540 1,515 7,623 Total assets 426,793 580,543 126,870 997,852 2,132,058 Capital expenditures 822 6,825 1,899 1,426 10,972 Six Months Ended June 30, 2018 Revenues $ 475,306 $ 497,379 $ 191,334 $ 3,625 $ 1,167,644 Adjusted EBITDA 53,993 170,399 27,510 (61,604 ) 190,298 Depreciation, depletion and amortization 16,727 35,003 7,536 986 60,252 Accretion on asset retirement obligation 9,771 937 1,130 2,147 13,985 Total assets 379,613 551,012 134,319 884,469 1,949,413 Capital expenditures 3,763 17,728 3,765 4,793 30,049 Six Months Ended June 30, 2017 Revenues $ 504,007 $ 453,232 $ 193,545 $ 57 $ 1,150,841 Adjusted EBITDA 79,794 130,862 54,152 (47,989 ) 216,819 Depreciation, depletion and amortization 18,085 37,149 6,485 903 62,622 Accretion on asset retirement obligation 10,080 1,057 1,080 3,029 15,246 Total assets 426,793 580,543 126,870 997,852 2,132,058 Capital expenditures 950 11,436 2,640 1,896 16,922
Reconciliation Statement of Segment Income from Operations to Consolidated Income Before Income Taxes	A reconciliation of net income to adjusted EBITDA follows: Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 (In thousands) Net income $ 43,306 $ 37,160 $ 103,291 $ 88,828 Provision for (benefit from) income taxes $ (3,366 ) $ 319 $ (3,910 ) $ 1,159 Interest expense, net 3,498 5,161 7,620 14,059 Depreciation, depletion and amortization 30,549 30,701 60,252 62,622 Accretion on asset retirement obligations 6,993 7,623 13,985 15,246 Amortization of sales contracts, net 3,248 14,352 6,299 29,042 Net loss resulting from early retirement of debt and debt restructuring 485 31 485 2,061 Non-service related pension and postretirement benefit costs (68 ) 232 1,235 953 Reorganization items, net 740 21 1,041 2,849 Adjusted EBITDA $ 85,385 $ 95,600 $ 190,298 $ 216,819

Revenue Recognition (Tables)

Revenue Recognition (Tables)	6 Months Ended
	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Schedule of effects of revenue recognition	PRB MET Other Thermal Corporate, Other and Eliminations Consolidated (in thousands) Three Months Ended June 30, 2018 North America revenues $ 229,035 $ 38,323 $ 40,547 $ 3,625 $ 311,530 Seaborne revenues 843 220,709 59,267 — 280,819 Total revenues $ 229,878 $ 259,032 $ 99,814 $ 3,625 $ 592,349 Three Months Ended June 30, 2017 North America revenues $ 230,579 $ 82,498 $ 71,539 $ (1 ) $ 384,615 Seaborne revenues — 145,151 20,100 — 165,251 Total revenues $ 230,579 $ 227,649 $ 91,639 $ (1 ) $ 549,866 PRB MET Other Thermal Corporate, Other and Eliminations Consolidated (in thousands) Six Months Ended June 30, 2018 North America revenues $ 473,395 $ 68,001 $ 84,214 $ 3,625 $ 629,235 Seaborne revenues 1,911 429,378 107,120 — 538,409 Total revenues $ 475,306 $ 497,379 $ 191,334 $ 3,625 $ 1,167,644 Six Months Ended June 30, 2017 North America revenues $ 504,007 $ 151,233 $ 140,503 $ 57 $ 795,800 Seaborne revenues — 301,999 53,042 — 355,041 Total revenues $ 504,007 $ 453,232 $ 193,545 $ 57 $ 1,150,841

Accounting Policies - Cash used

Accounting Policies - Cash used in investing activities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Condensed Cash Flow Statements, Captions [Line Items]
Cash used in investing activities			$ (35,326)	$ (98,210)
Cost of sales	$ 474,388	$ 434,465	929,168	894,915
Selling, general and administrative expenses	$ 24,756	22,456	$ 50,704	43,218
Accounting Standards Update 2016-08
Condensed Cash Flow Statements, Captions [Line Items]
Cost of sales		(600)		(1,500)
Selling, general and administrative expenses		$ 300		500
Cash used in investing activities previously reported
Condensed Cash Flow Statements, Captions [Line Items]
Cash used in investing activities				(68,915)
Withdrawals of restricted cash | Accounting Standards Update 2016-08
Condensed Cash Flow Statements, Captions [Line Items]
Cash used in investing activities				$ 29,295

Accumulated Other Comprehensi43

Accumulated Other Comprehensive Income (Schedule of Accumulated Other Comprehensive Income (Loss)) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018USD ($)
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	$ 665,865
Unrealized gains (losses)	(689)
Amounts reclassified from AOCI	(1,875)
Ending Balance	640,948
Accumulated Other Comprehensive Income
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	20,367
Ending Balance	17,803
Derivative instruments
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	647
Unrealized gains (losses)	(5,248)
Amounts reclassified from AOCI	(488)
Ending Balance	(5,089)
Pension, Postretirement and Other Postemployment Benefits
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	19,720
Unrealized gains (losses)	5,024
Amounts reclassified from AOCI	(1,371)
Ending Balance	23,373
Available-for-sale securities
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	0
Unrealized gains (losses)	(465)
Amounts reclassified from AOCI	(16)
Ending Balance	$ (481)

Accumulated Other Comprehensi44

Accumulated Other Comprehensive Income (Schedule of Reclassifications) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	$ 592,349	$ 549,866	$ 1,167,644	$ 1,150,841
Interest expense	(5,050)	(6,003)	(10,445)	(15,428)
Pension settlement	68	(232)	(1,235)	(953)
Provision for (benefit from) income taxes	3,366	(319)	3,910	(1,159)
Net income	43,306	37,160	103,291	88,828
Reclassification out of Accumulated Other Comprehensive Income | Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	0	0	0	0
Interest expense	348	0	488	0
Provision for (benefit from) income taxes	0	0	0	0
Net income	348	0	488	0
Reclassification out of Accumulated Other Comprehensive Income | Pension, Postretirement and Other Postemployment Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension settlement	1,371	487	1,371	487
Provision for (benefit from) income taxes	0	0	0	0
Net income	1,371	487	1,371	487
Reclassification out of Accumulated Other Comprehensive Income | Pension settlement
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension settlement	1,371	487	1,371	487
Reclassification out of Accumulated Other Comprehensive Income | Available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and investment income	16	0	16	332
Provision for (benefit from) income taxes	0	0	0	0
Net income	$ 16	$ 0	$ 16	$ 332

Reorganization items, net (Narr

Reorganization items, net (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Discontinued Operations and Disposal Groups [Abstract]
Reorganization items, net	$ (740)	$ (21)	$ (1,041)	$ (2,849)
Payments for reorganization items	$ 300	$ 900	$ 600	$ 4,700

Inventories (Details)

Inventories (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Coal	$ 72,268	$ 54,692
Repair parts and supplies	84,937	74,268
Inventories	157,205	128,960
Allowance for slow-moving and obsolete inventories	$ (900)	$ (300)

Investments in Available-for-47

Investments in Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Cost Basis	$ 161,374	$ 156,189
Available-for-sale, Gains	6	22
Available-for-sale, Losses	(486)	(365)
Available-for-sale, Fair Value	160,894	155,846
Available-for-sale, Short-Term Investments	160,894	155,846
Short-term Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Short-Term Investments	160,894	155,846
Other Assets
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Other Assets	0	0
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Cost Basis	88,858	64,151
Available-for-sale, Gains	3	22
Available-for-sale, Losses	(161)	(73)
Available-for-sale, Fair Value	88,700	64,100
U.S. government and agency securities | Short-term Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Short-Term Investments	88,700	64,100
U.S. government and agency securities | Other Assets
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Other Assets	0	0
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Cost Basis	72,516	92,038
Available-for-sale, Gains	3	0
Available-for-sale, Losses	(325)	(292)
Available-for-sale, Fair Value	72,194	91,746
Corporate notes and bonds | Short-term Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Short-Term Investments	72,194	91,746
Corporate notes and bonds | Other Assets
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Other Assets	$ 0	$ 0

Investments in Available-for-48

Investments in Available-for-Sale Securities (Narrative) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Abstract]
Unrealized losses owned for less than 12 months	$ 128.1	$ 132
Unrealized losses owned for greater than 12 months	$ 17.5	$ 0

Sales Contracts (Schedule of Sa

Sales Contracts (Schedule of Sales Contracts) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Original fair value, Assets	$ 97,196	$ 97,196
Original fair value, Liabilities	31,742	31,742
Accumulated amortization, Asset	(91,650)	(84,760)
Accumulated amortization, Liabilities	(30,570)	(29,979)
Total, Assets	5,546	12,436
Total, Liabilities	1,172	1,763
Net Total	4,374	10,673
Liabilities	634	934
Other current Assets
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Assets	5,544	12,432
Other Current Liabilities
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Liabilities	634	934
Other Noncurrent Assets
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Assets	2	4
Other Noncurrent Liabilities
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Liabilities	$ 538	$ 829

Derivatives (Narrative) (Detail

Derivatives (Narrative) (Details) gal in Millions, $ in Millions	6 Months Ended
	Dec. 31, 2018USD ($)	Jun. 30, 2018USD ($)$ / optiongal	Dec. 31, 2017USD ($)
Derivative [Line Items]
Current asset representing cash collateral posted | $		$ 41.1	$ 16.2
Derivative contracts expected to be reclassified from OCI into earnings | $		$ (7.5)
Not Designated as Hedging Instrument | Heating Oil
Derivative [Line Items]
Percent of expected requirements covered		70.00%
Derivative, average price risk option strike price (in usd per gallon) | $ / option		2.10
Not Designated as Hedging Instrument | Diesel Purchases
Derivative [Line Items]
Percent of expected requirements covered		50.00%
Derivative, average price risk option strike price (in usd per gallon) | $ / option		2.33
Not Designated as Hedging Instrument | Diesel Purchases | Heating Oil
Derivative [Line Items]
Quantities under derivative contracts (in gallons) | gal		26
Not Designated as Hedging Instrument | Diesel Purchases | Minimum
Derivative [Line Items]
Diesel fuel purchased annually (in gallons) | gal		40
Not Designated as Hedging Instrument | Diesel Purchases | Maximum
Derivative [Line Items]
Diesel fuel purchased annually (in gallons) | gal		47
Scenario, Forecast
Derivative [Line Items]
Value of trading portfolio realized | $	$ (0.4)

Derivatives (Schedule of Price

Derivatives (Schedule of Price Risk Derivatives) (Details) T in Thousands	6 Months Ended
	Jun. 30, 2018T
Coal sales
Derivative [Line Items]
Derivatives held (in tons)	2,676
Coal purchases
Derivative [Line Items]
Derivatives held (in tons)	512
2018 | Coal sales
Derivative [Line Items]
Derivatives held (in tons)	1,089
2018 | Coal purchases
Derivative [Line Items]
Derivatives held (in tons)	433
2019 | Coal sales
Derivative [Line Items]
Derivatives held (in tons)	1,587
2019 | Coal purchases
Derivative [Line Items]
Derivatives held (in tons)	79

Derivatives (Disclosure Of Fair

Derivatives (Disclosure Of Fair Value Of Derivatives) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative Assets	$ 50,409	$ 55,550
Derivative Liabilities	(68,611)	(57,259)
Effect of counterparty netting in derivative assets	(42,542)	(50,042)
Effect of counterparty netting in derivative liabilities	42,542	50,042
Derivative Asset	7,867	5,508
Derivative Liability	(26,069)	(7,217)
Net derivatives as classified in the balance sheets	(18,202)	(1,709)
Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative Assets	48,646	54,608
Derivative Liabilities	(59,223)	(55,113)
Not Designated as Hedging Instrument | Coal Contract
Derivative [Line Items]
Derivative Assets	35,894	44,088
Derivative Liabilities	(36,323)	(45,221)
Coal Contract | Designated as Hedging Instrument
Derivative [Line Items]
Derivative Assets	1,763	942
Derivative Liabilities	(9,388)	(2,146)
Coal Contract | Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative Assets	6,058	5,139
Derivative Liabilities	(22,900)	(9,892)
Heating oil — diesel purchases | Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative Assets	6,652	5,354
Derivative Liabilities	0	0
Natural gas | Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative Assets	42	27
Derivative Liabilities	$ 0	$ 0

Derivatives (Net Derivatives As

Derivatives (Net Derivatives As Reflected On The Balance Sheets) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Net derivatives as classified in the balance sheet	$ (18,202)	$ (1,709)
Accrued expenses and other current liabilities
Derivatives, Fair Value [Line Items]
Net derivatives as classified in the balance sheet	(26,069)	(7,217)
Heating oil and coal | Other current assets
Derivatives, Fair Value [Line Items]
Net derivatives as classified in the balance sheet	$ 7,867	$ 5,508

Derivatives (Effects Of Derivat

Derivatives (Effects Of Derivatives On Measures Of Financial Performance) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Change in fair value of coal derivatives and coal trading activities, net	$ (15,138)	$ (863)	$ (11,724)	$ (1,717)
Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income (Effective Portion)	(12,757)	15	(8,068)	35
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion)	0		0
Designated as Hedging Instrument | Coal sales | Coal Contract | Coal sales
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income (Effective Portion)	(15,462)	49	(10,231)	269
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion)	0	0	0	0
Designated as Hedging Instrument | Coal purchases | Coal Contract | Coal purchases
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income (Effective Portion)	2,705	(34)	2,163	(234)
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion)	0		0
Not Designated as Hedging Instrument | Coal Contract | Coal and natural gas realized and unrealized
Derivative Instruments, Gain (Loss) [Line Items]
Realized and Unrealized Gain (Loss) on Derivatives	384	(836)	942	(1,494)
Unrealized Gain (Loss) on Derivatives	(15,505)	0	(12,630)	26
Not Designated as Hedging Instrument | Coal Contract | Other operating (income) expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gain (Loss) on Derivatives	(1,649)	0	(2,680)	0
Not Designated as Hedging Instrument | Natural gas | Coal and natural gas realized and unrealized
Derivative Instruments, Gain (Loss) [Line Items]
Realized and Unrealized Gain (Loss) on Derivatives	(17)	(27)	(36)	(249)
Not Designated as Hedging Instrument | Heating oil — diesel purchases | Other operating (income) expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Heating oil realized and unrealized gains and losses	$ 3,657	$ (1,147)	$ 3,675	$ (4,725)

Accrued Expenses and Other Cu55

Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Payroll and employee benefits	$ 41,627	$ 53,149
Taxes other than income taxes	78,501	77,017
Interest	204	246
Acquired sales contracts	634	934
Workers’ compensation	19,664	18,782
Asset retirement obligations	19,840	19,840
Other	34,260	14,193
Accrued expenses and other current liabilities	$ 194,730	$ 184,161

Debt and Financing Arrangemen56

Debt and Financing Arrangements (Long term Debt) (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Other	$ 29,280,000	$ 36,514,000
Debt issuance costs	(6,619,000)	(7,032,000)
Total	317,690,000	325,917,000
Less: current maturities of debt	12,533,000	15,783,000
Long-term debt	305,157,000	310,134,000
Term loan due 2024 ($296.3 million face value)
Debt Instrument [Line Items]
Term loan	295,029,000	$ 296,435,000
Debt instrument, face amount	$ 296,300,000

Debt and Financing Arrangemen57

Debt and Financing Arrangements (Narrative) (Details) - USD ($)	Apr. 03, 2018	Sep. 25, 2017	Apr. 27, 2017	Mar. 07, 2017	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Line of Credit Facility [Line Items]
Fair value of derivative assets					$ 50,409,000	$ 50,409,000		$ 55,550,000
Debt financing costs						529,000	$ 8,900,000
Debt restructuring costs						50,000	2,061,000
Interest Rate Swap
Line of Credit Facility [Line Items]
Interest rate swaps settlements gains					300,000	500,000
Other Noncurrent Assets | Interest Rate Swap
Line of Credit Facility [Line Items]
Fair value of derivative assets					$ 4,200,000	4,200,000
Senior Notes | New Term Loan Debt Facility
Line of Credit Facility [Line Items]
Debt instrument, face amount		$ 300,000,000
Basis spread on variable rate		3.25%
Call premium rate		1.00%
Net cash proceeds of from debt issuances and other non-ordinary sales or dispositions (percent)				100.00%
Default to indebtedness				$ 50,000,000
Default to surety, reclamation or similar bond				50,000,000
Default to uninsured judgment				50,000,000
Uninsured losses or proceedings against				50,000,000
Debt financing costs						500,000
Senior Notes | New Term Loan Debt Facility | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.75%	1.00%
Basis spread on variable rate, floor	1.00%
Call premium rate	1.00%
Senior Notes | New Term Loan Debt Facility | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.75%
Line of Credit | Superpriority Debtor-in Possession Credit Agreement
Line of Credit Facility [Line Items]
Debt financing costs							$ 8,900,000
New Term Loan Debt Facility | Senior Notes
Line of Credit Facility [Line Items]
Debt instrument, face amount				$ 300,000,000
Percentage of face amount				99.50%
Quarterly amortization payments				$ 750,000
Amount of voting equity interests of domestic subsidiaries guaranteed (percent)				100.00%
Amount of voting equity interests of foreign owned subsidiaries guaranteed (percent)				65.00%
New Term Loan Debt Facility | Senior Notes | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate					2.75%
New Term Loan Debt Facility | Senior Notes | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate		2.25%
Line of Credit | Secured Debt
Line of Credit Facility [Line Items]
Current borrowing capacity					$ 79,500,000	79,500,000
Letters of credit outstanding					75,300,000	75,300,000
Line of Credit | Secured Debt | Regions Bank
Line of Credit Facility [Line Items]
Debt instrument, face amount			$ 40,000,000
Maximum borrowing capacity			200,000,000
Current borrowing capacity					160,000,000	160,000,000
Covenant minimum amount			$ 175,000,000
Letters of credit outstanding					35,200,000	35,200,000
Percentage of coal inventory borrowing base			85.00%
Percentage of parts and supplies inventory borrowing base			85.00%
Percentage of clause borrowing base			35.00%
Percent of eligible cash			100.00%
Covenant amount (less than)			$ 250,000,000
Additional availability for borrowings					$ 4,800,000	$ 4,800,000
Line of Credit | Secured Debt | LIBOR | Regions Bank | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate			2.25%
Line of Credit | Secured Debt | LIBOR | Regions Bank | Maximum
Line of Credit Facility [Line Items]
Percentage of clause borrowing base			2.50%
Line of Credit | Secured Debt | Base Rate | Regions Bank | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate			1.25%
Line of Credit | Secured Debt | Base Rate | Regions Bank | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate			1.50%

Debt and Financing Arrangemen58

Debt and Financing Arrangements (Interest rate derivatives) (Details) $ in Millions	Jun. 30, 2018USD ($)
Interest rate swap, effective 2018
Debt Instrument [Line Items]
Notional Amount	$ 250
Fixed Rate	1.662%
Interest rate swap, effective 2019
Debt Instrument [Line Items]
Notional Amount	$ 200
Fixed Rate	1.952%
Interest rate swap, effective 2020
Debt Instrument [Line Items]
Notional Amount	$ 100
Fixed Rate	2.182%

Income Taxes (Income Tax Expens

Income Taxes (Income Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Income tax provision (benefit) at statutory rate	$ 8,387	$ 13,118	$ 20,870	$ 31,496
Percentage depletion allowance	(2,488)	(5,692)	(7,095)	(12,731)
State taxes, net of effect of federal taxes	583	408	1,337	891
Change in valuation allowance	(7,317)	(8,316)	(17,956)	(20,218)
Other, net	(2,531)	801	(1,066)	1,721
Provision for (benefit from) income taxes	(3,366)	$ 319	(3,910)	$ 1,159
Reversal of reserve	$ 3,300		$ 3,300

Fair Value Measurements (Summar

Fair Value Measurements (Summary Of Financial Assets And Liabilities Accounted For At Fair Value) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets:
Investments in marketable securities	$ 160,894	$ 155,846
Derivatives	12,031
Total assets	172,925
Liabilities:
Derivatives	26,069	$ 7,217
Level 1
Assets:
Investments in marketable securities	54,832
Derivatives	593
Total assets	55,425
Liabilities:
Derivatives	24,862
Level 2
Assets:
Investments in marketable securities	106,062
Derivatives	4,786
Total assets	110,848
Liabilities:
Derivatives	638
Level 3
Assets:
Investments in marketable securities	0
Derivatives	6,652
Total assets	6,652
Liabilities:
Derivatives	$ 569

Fair Value Measurements (Summ61

Fair Value Measurements (Summary Of Change In The Fair Values Of Financial Instruments Categorized As Level 3) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	$ 4,969	$ 5,426
Realized and unrealized gains recognized in earnings, net	3,628	3,653
Purchases	823	1,656
Issuances	(580)	(654)
Settlements	(2,757)	(3,998)
Ending balance	$ 6,083	$ 6,083

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of senior notes and other long-term debt, including amounts classified as current	$ 327.1	$ 327.1	$ 336.1
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net unrealized gains (losses) related to level 3 financial instruments	$ 1.5	$ 3

Earnings per Common Share (Weig

Earnings per Common Share (Weighted-Average Number of Shares) (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Weighted average shares outstanding:
Basic weighted average shares outstanding (in shares)	20,156	24,659	20,529	24,834
Effect of dilutive securities (in shares)	880	423	927	411
Diluted weighted average shares outstanding (in shares)	21,036	25,082	21,456	25,245

Workers Compensation Expense (W

Workers Compensation Expense (Workers Compensation Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Occupational disease
Accrued Workers Compensation [Line Items]
Service cost	$ 1,860	$ 1,559	$ 3,720	$ 3,117
Interest cost	1,194	1,168	2,389	2,337
Net benefit credit	3,054	2,727	6,109	5,454
Traumatic injury claims and assessments
Accrued Workers Compensation [Line Items]
Traumatic injury claims and assessments	2,188	2,532	5,199	5,410
Total workers’ compensation expense
Accrued Workers Compensation [Line Items]
Total workers’ compensation expense	$ 5,242	$ 5,259	$ 11,308	$ 10,864

Employee Benefit Plans (Pension

Employee Benefit Plans (Pension And Other Postretirement Benefit Costs) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined benefit pension plan
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 2,270	$ 2,991	$ 4,541	$ 5,982
Expected return on plan assets	(3,080)	(4,499)	(6,161)	(8,996)
Pension Settlement	(1,371)	(487)	(1,371)	(487)
Net benefit credit	(2,181)	(1,995)	(2,991)	(3,501)
Other postretirement benefits plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	139	171	279	341
Interest cost	919	1,059	1,837	2,117
Net benefit credit	$ 1,058	$ 1,230	$ 2,116	$ 2,458

Employee Benefit Plans Narrativ

Employee Benefit Plans Narrative (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Decrease in defined benefit plan obligation	$ 106,934	$ 102,369
Defined benefit pension plan
Defined Benefit Plan Disclosure [Line Items]
Cash balance revaluation discount rate	4.11%
Change in assumptions for defined benefit plans | Defined benefit pension plan
Defined Benefit Plan Disclosure [Line Items]
Decrease in defined benefit plan obligation	$ 5,000

Commitments and Contingencies (

Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Amount accrued	$ 0.4	$ 0.2

Segment Information (Schedule O

Segment Information (Schedule Of Operating Segment Results) (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018USD ($)	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)Segment	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Segment Reporting [Abstract]
Number of reportable segments | Segment			2
Segment Reporting Information [Line Items]
Revenues	$ 592,349	$ 549,866	$ 1,167,644	$ 1,150,841
Adjusted EBITDA	85,385	95,600	190,298	216,819
Depreciation, depletion and amortization	30,549	30,701	60,252	62,622
Accretion on asset retirement obligations	6,993	7,623	13,985	15,246
Total assets	1,949,413	2,132,058	1,949,413	2,132,058	$ 1,979,632
Capital expenditures	20,596	10,972	30,049	16,922
Operating Segments | PRB
Segment Reporting Information [Line Items]
Revenues	229,878	230,579	475,306	504,007
Adjusted EBITDA	26,491	31,789	53,993	79,794
Depreciation, depletion and amortization	8,304	8,574	16,727	18,085
Accretion on asset retirement obligations	4,885	5,040	9,771	10,080
Total assets	379,613	426,793	379,613	426,793
Capital expenditures	3,065	822	3,763	950
Operating Segments | MET
Segment Reporting Information [Line Items]
Revenues	259,032	227,649	497,379	453,232
Adjusted EBITDA	86,657	62,552	170,399	130,862
Depreciation, depletion and amortization	18,018	18,385	35,003	37,149
Accretion on asset retirement obligations	469	528	937	1,057
Total assets	551,012	580,543	551,012	580,543
Capital expenditures	11,899	6,825	17,728	11,436
Operating Segments | Other Thermal
Segment Reporting Information [Line Items]
Revenues	99,814	91,639	191,334	193,545
Adjusted EBITDA	11,842	26,910	27,510	54,152
Depreciation, depletion and amortization	3,701	3,285	7,536	6,485
Accretion on asset retirement obligations	565	540	1,130	1,080
Total assets	134,319	126,870	134,319	126,870
Capital expenditures	2,559	1,899	3,765	2,640
Corporate, Other and Eliminations
Segment Reporting Information [Line Items]
Revenues	3,625	(1)	3,625	57
Adjusted EBITDA	(39,605)	(25,651)	(61,604)	(47,989)
Depreciation, depletion and amortization	526	457	986	903
Accretion on asset retirement obligations	1,074	1,515	2,147	3,029
Total assets	884,469	997,852	884,469	997,852
Capital expenditures	$ 3,073	$ 1,426	$ 4,793	$ 1,896

Segment Information (Reconcilia

Segment Information (Reconciliation Statement Of Segment Income from Operations To Consolidated Income Before Income Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting [Abstract]
Net income	$ 43,306	$ 37,160	$ 103,291	$ 88,828
Provision for (benefit from) income taxes	(3,366)	319	(3,910)	1,159
Interest expense, net	3,498	5,161	7,620	14,059
Depreciation, depletion and amortization	30,549	30,701	60,252	62,622
Accretion on asset retirement obligations	6,993	7,623	13,985	15,246
Amortization of sales contracts, net	3,248	14,352	6,299	29,042
Net loss resulting from early retirement of debt and debt restructuring	485	31	485	2,061
Non-service related pension and postretirement benefit costs	(68)	232	1,235	953
Reorganization items, net	740	21	1,041	2,849
Adjusted EBITDA	$ 85,385	$ 95,600	$ 190,298	$ 216,819

Revenue Recognition (Details)

Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 592,349	$ 549,866	$ 1,167,644	$ 1,150,841
Corporate, Other and Eliminations
Disaggregation of Revenue [Line Items]
Revenues	3,625	(1)	3,625	57
North America revenues
Disaggregation of Revenue [Line Items]
Revenues	311,530	384,615	629,235	795,800
North America revenues | Corporate, Other and Eliminations
Disaggregation of Revenue [Line Items]
Revenues	3,625	(1)	3,625	57
Seaborne revenues
Disaggregation of Revenue [Line Items]
Revenues	280,819	165,251	538,409	355,041
Seaborne revenues | Corporate, Other and Eliminations
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
PRB | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	229,878	230,579	475,306	504,007
PRB | North America revenues | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	229,035	230,579	473,395	504,007
PRB | Seaborne revenues | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	843	0	1,911	0
MET | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	259,032	227,649	497,379	453,232
MET | North America revenues | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	38,323	82,498	68,001	151,233
MET | Seaborne revenues | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	220,709	145,151	429,378	301,999
Other Thermal | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	99,814	91,639	191,334	193,545
Other Thermal | North America revenues | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	40,547	71,539	84,214	140,503
Other Thermal | Seaborne revenues | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	$ 59,267	$ 20,100	$ 107,120	$ 53,042

Revenue Recognition - Narrative

Revenue Recognition - Narrative (Details) T in Millions	Jun. 30, 2018T
Revenue from Contract with Customer [Abstract]
Remaining performance obligations, fixed price contracts (in tons)	70.8
Remaining performance obligations, variable price contracts (in tons)	6.4
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-07-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligations, fixed price contracts (in tons)	35
Remaining performance obligations, variable price contracts (in tons)	4.9

Subsequent Events (Narrative) (

Subsequent Events (Narrative) (Details) - USD ($)	6 Months Ended
	Jun. 30, 2018	Jul. 27, 2018	Jul. 26, 2018
Subsequent Event [Line Items]
Shares repurchased (in shares)	5,344,411
Average share price (in dollars per share)	$ 78.40
Aggregate purchase price	$ 419,000,000
Subsequent Event
Subsequent Event [Line Items]
Increase to the share repurchase program			$ 250,000,000
Total authorization of share repurchase program			$ 750,000,000
Common shares outstanding (in shares)		19,587,748

Uncategorized Items - aci-20180

Label	Element	Value
Restricted Cash and Cash Equivalents, Current	us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue	$ 41,755,000
Restricted Cash and Cash Equivalents, Current	us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue	$ 0