Arch Resources (ARCH) 10-Q23 Oct 182018 Q3 Quarterly reportFinancial data

Company Profile

Document And Entity Information

Document And Entity Information - shares	9 Months Ended
Document And Entity Information - shares	Sep. 30, 2018	Oct. 19, 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	Sep. 30, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		18,799,400

Condensed Consolidated Income S

Condensed Consolidated Income Statements - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Revenues	$ 633,180	$ 613,538	$ 1,800,824	$ 1,764,379
Costs, expenses and other operating
Cost of sales (exclusive of items shown separately below)	482,029	494,379	1,411,197	1,389,294
Depreciation, depletion and amortization	31,775	31,914	92,027	94,536
Accretion on asset retirement obligations	6,992	7,580	20,977	22,826
Amortization of sales contracts, net	3,241	13,861	9,540	42,903
Change in fair value of coal derivatives and coal trading activities, net	10,418	1,028	22,142	2,745
Selling, general and administrative expenses	22,909	21,290	73,613	64,508
Gain on sale of Lone Mountain Processing, Inc.	0	(21,574)	0	(21,574)
Other operating income, net	(7,070)	(8,250)	(21,320)	(14,078)
Costs, expenses and other operating	550,294	540,228	1,608,176	1,581,160
Income from operations	82,886	73,310	192,648	183,219
Interest expense, net
Interest expense	(5,179)	(5,972)	(15,624)	(21,400)
Interest and investment income	1,801	720	4,626	2,089
Interest expense, net	(3,378)	(5,252)	(10,998)	(19,311)
Income before nonoperating expenses	79,508	68,058	181,650	163,908
Nonoperating expenses
Non-service related pension and postretirement benefit costs	(971)	(821)	(2,206)	(1,774)
Net loss resulting from early retirement of debt and debt restructuring	0	(486)	(485)	(2,547)
Reorganization items, net	(560)	(43)	(1,601)	(2,892)
Nonoperating expenses	(1,531)	(1,350)	(4,292)	(7,213)
Income before income taxes	77,977	66,708	177,358	156,695
Benefit from income taxes	(45,215)	(1,643)	(49,125)	(484)
Net income	$ 123,192	$ 68,351	$ 226,483	$ 157,179
Net income per common share
Basic earnings per common share (in dollars per share)	$ 6.40	$ 2.90	$ 11.27	$ 6.44
Diluted earnings per common share (in dollars per share)	$ 6.10	$ 2.83	$ 10.76	$ 6.32
Weighted average shares outstanding
Basic weighted average shares outstanding (in shares)	19,250	23,580	20,102	24,416
Diluted weighted average shares outstanding (in shares)	20,208	24,135	21,040	24,875
Dividends declared per common share (in dollars per share)	$ 0.4	$ 0.35	$ 1.2	$ 0.7

Condensed Consolidated Statemen

Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income	$ 123,192	$ 68,351	$ 226,483	$ 157,179
Derivative instruments
Comprehensive income (loss) before tax	64	(19)	(5,672)	257
Income tax benefit (provision)	0	0	0	0
Other comprehensive income (loss), derivative instruments, net of tax	64	(19)	(5,672)	257
Pension, postretirement and other post-employment benefits
Comprehensive income (loss) before tax	2,736	(8,521)	6,389	(5,367)
Income tax benefit (provision)	0	0	0	0
Other comprehensive income (loss), pension, postretirement and other post-employment benefits, net of tax	2,736	(8,521)	6,389	(5,367)
Available-for-sale securities
Comprehensive income (loss) before tax	102	0	(379)	(387)
Income tax benefit (provision)	0	0	0	0
Other comprehensive income (loss), available-for-sale securities, net of tax	102	0	(379)	(387)
Total other comprehensive income (loss)	2,902	(8,540)	338	(5,497)
Total comprehensive income	$ 126,094	$ 59,811	$ 226,821	$ 151,682

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 245,679	$ 273,387
Short term investments	162,530	155,846
Trade accounts receivable	183,318	172,604
Other receivables	26,972	29,771
Inventories	163,878	128,960
Other current assets	95,040	70,426
Total current assets	877,417	830,994
Property, plant and equipment, net	919,613	955,948
Other assets
Equity investments	105,325	106,107
Other noncurrent assets	95,267	86,583
Total other assets	200,592	192,690
Total assets	1,997,622	1,979,632
Current Liabilities
Accounts payable	119,629	134,137
Accrued expenses and other current liabilities	203,667	184,161
Current maturities of debt	11,478	15,783
Total current liabilities	334,774	334,081
Long-term debt	302,830	310,134
Asset retirement obligations	319,601	308,855
Accrued pension benefits	5,101	14,036
Accrued postretirement benefits other than pension	105,400	102,369
Accrued workers’ compensation	180,880	184,835
Other noncurrent liabilities	61,896	59,457
Total liabilities	1,310,482	1,313,767
Stockholders' equity
Common stock, $0.01 par value, authorized 300,000 shares, issued 25,047 shares at September 30, 2018 and December 31, 2017, respectively	250	250
Paid-in capital	712,295	700,125
Retained earnings	449,122	247,232
Treasury stock, 6,215 shares and 3,977 shares at September 30, 2018 and December 31, 2017, respectively, at cost	(495,232)	(302,109)
Accumulated other comprehensive income	20,705	20,367
Total stockholders’ equity	687,140	665,865
Total liabilities and stockholders’ equity	$ 1,997,622	$ 1,979,632

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	25,047,000	25,047,000
Treasury stock, shares (in shares)	6,215,000	3,977,000

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities
Net income	$ 226,483	$ 157,179
Adjustments to reconcile to cash provided by operating activities:
Depreciation, depletion and amortization	92,027	94,536
Accretion on asset retirement obligations	20,977	22,826
Amortization of sales contracts, net	9,540	42,903
Prepaid royalties expensed	134	2,905
Deferred income taxes	(22,999)	6,069
Employee stock-based compensation expense	12,161	7,485
Gains on disposals and divestitures, net	(54)	(23,006)
Net loss resulting from early retirement of debt and debt restructuring	485	2,547
Amortization relating to financing activities	3,300	2,628
Changes in:
Receivables	(5,983)	(24,110)
Inventories	(34,918)	(13,102)
Accounts payable, accrued expenses and other current liabilities	(24,762)	5,103
Income taxes, net	(1,942)	(2,430)
Other	(8,334)	20,612
Cash provided by operating activities	266,115	302,145
Investing activities
Capital expenditures	(55,742)	(30,503)
Minimum royalty payments	(522)	(5,033)
Proceeds from disposals and divestitures	512	11,432
Purchases of short term investments	(140,097)	(191,327)
Proceeds from sales of short term investments	133,400	123,996
Investments in and advances to affiliates, net	(1,817)	(9,216)
Cash used in investing activities	(64,266)	(100,651)
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	(2,250)	(1,500)
Net payments on other debt	(10,286)	(5,992)
Debt financing costs	(1,009)	(10,043)
Net loss resulting from early retirement of debt and debt restructuring	(50)	(2,360)
Dividends paid	(23,966)	(16,763)
Purchases of treasury stock	(192,221)	(215,735)
Other	10
Cash used in financing activities	(229,772)	(279,577)
Decrease in cash and cash equivalents, including restricted cash	(27,923)	(78,083)
Cash and cash equivalents, including restricted cash, beginning of period	273,602	376,422
Cash and cash equivalents, including restricted cash, end of period	$ 245,679	$ 298,339

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - Supplemental Information - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Cash and cash equivalents, including restricted cash, end of period
Cash and cash equivalents	$ 245,679	$ 298,337
Restricted cash	0	2
Cash and cash equivalents, including restricted cash	$ 245,679	$ 298,339

Basis of Presentation

Basis of Presentation	9 Months Ended
Basis of Presentation	Sep. 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 nine months ended September 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	9 Months Ended
Accounting Policies	Sep. 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 19 , “ 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 nine months ended September 30, 2017 was adjusted to exclude the change in restricted cash as follows: (in thousands) Nine Months Ended September 30, 2017 Cash used in investing activities previously reported $ (29,603 ) Less: Withdrawals of restricted cash 71,048 Cash used in investing activities $ (100,651 ) 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 $1.0 million and $2.6 million reduction in cost of coal sales and a $0.2 million and $0.8 million increase in selling, general and administrative costs with the corresponding offset to Nonoperating expense for the three and nine months ended September 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. The Company expects 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 fourth quarter of 2018, although it does 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	9 Months Ended
Accumulated Other Comprehensive Income	Sep. 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) (9,743 ) 8,373 (355 ) (1,725 ) Amounts reclassified from AOCI 4,071 (1,984 ) (24 ) 2,063 Balance at September 30, 2018 $ (5,025 ) $ 26,109 $ (379 ) $ 20,705 The following amounts were reclassified out of AOCI: Three Months Ended September 30, Nine Months Ended September 30, Details About AOCI Components 2018 2017 2018 2017 Line Item in the Condensed Consolidated Statement of Operations (In thousands) Coal hedges $ (4,824 ) $ (88 ) $ (4,824 ) $ (88 ) Revenues Interest rate hedges 265 — 753 — Interest expense $ (4,559 ) $ (88 ) $ (4,071 ) $ (88 ) Net of tax Pension, postretirement and other post-employment benefits Pension settlement 613 228 1,984 715 Non-service related pension and postretirement benefit (costs) credits Actuarial curtailments — (773 ) — (773 ) Sale of Cumberland River Pension Plan — (360 ) — (360 ) $ 613 $ (905 ) $ 1,984 $ (418 ) Net of tax Available-for-sale securities $ 8 $ — $ 24 $ 332 Interest and investment income $ 8 $ — $ 24 $ 332 Net of tax

Divestitures

Divestitures	9 Months Ended
Divestitures	Sep. 30, 2018
Discontinued Operations and Disposal Groups [Abstract]
Divestitures	Divestitures 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, and two idled mining companies, Cumberland River Coal LLC and Powell Mountain Energy LLC to Revelation Energy LLC. The Company received $8.3 million of proceeds offset by $1.3 million in disbursements related to landholder consent fees and professional fees; and recorded a gain of $21.6 million which is reflected as a separate line, “Gain on sale of Lone Mountain Processing, Inc.,” within the Condensed Consolidated Statement of Operations. The gain included a $4.7 million curtailment gain related to black lung liabilities accrued for active employees at these operations, $0.5 million curtailment gain related to postretirement medical claims.

Reorganization items, net

Reorganization items, net	9 Months Ended
Reorganization items, net	Sep. 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 September 30, 2018 and 2017 , the Company recorded $0.6 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 $0.6 million and $0.2 million during the three months ended September 30, 2018 and 2017 , respectively. During the nine months ended September 30, 2018 and 2017 , the Company recorded $1.6 million and $2.9 million , respectively in “Reorganization items, net” primarily comprised of professional fee expenses. Net cash paid for “Reorganization items, net” totaled $1.2 million and $4.8 million during the nine months ended September 30, 2018 and 2017 , respectively.

Inventories

Inventories	9 Months Ended
Inventories	Sep. 30, 2018
Inventory Disclosure [Abstract]
Inventories	Inventories Inventories consist of the following: September 30, December 31, 2018 2017 (In thousands) Coal $ 77,497 $ 54,692 Repair parts and supplies 86,381 74,268 $ 163,878 $ 128,960 The repair parts and supplies are stated net of an allowance for slow-moving and obsolete inventories of $1.0 million at September 30, 2018 and $0.3 million at December 31, 2017 .

Investments in Available-for-Sa

Investments in Available-for-Sale Securities	9 Months Ended
Investments in Available-for-Sale Securities	Sep. 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: September 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 $ 99,754 $ 1 $ (180 ) $ 99,575 $ 99,575 $ — Corporate notes and bonds 63,155 — (200 ) 62,955 62,955 — Total Investments $ 162,909 $ 1 $ (380 ) $ 162,530 $ 162,530 $ — 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 $151.6 million and $132.0 million at September 30, 2018 and December 31, 2017 , respectively. There were no investments with unrealized losses that were owned for over a year at September 30, 2018 and December 31, 2017 , respectively. The unrealized losses in the Company’s portfolio at September 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 September 30, 2018 have maturity dates ranging from the fourth quarter of 2018 through the second quarter of 2020 . 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	9 Months Ended
Sales Contracts	Sep. 30, 2018
Acquired Sales Contracts [Abstract]
Sales Contracts	Sales Contracts The sales contracts reflected in the Condensed Consolidated Balance Sheets are as follows: September 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 (95,104 ) (30,783 ) (84,760 ) (29,979 ) Total $ 2,092 $ 959 $ 1,133 $ 12,436 $ 1,763 $ 10,673 Balance Sheet classification: Other current $ 2,091 $ 562 $ 12,432 $ 934 Other noncurrent $ 1 $ 397 $ 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	9 Months Ended
Derivatives	Sep. 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 11 , “ 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 48 million gallons of diesel fuel for use in its operations annually. 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 September 30, 2018 , the Company had protected the price of approximately 69% of its expected diesel fuel purchases for the remainder of 2018 at an average strike price of $2.05 per gallon. Additionally, the Company has protected approximately 38% of its expected 2019 purchases with call options with an average strike price of $2.33 per gallon. At September 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 September 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 646 1,620 2,266 Coal purchases 284 118 402 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 $0.7 million of losses 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: September 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 $ 310 $ (7,979 ) $ 942 $ (2,146 ) Derivatives Not Designated as Hedging Instruments Heating oil -- diesel purchases 6,240 — 5,354 — Coal -- held for trading purposes 38,895 (40,006 ) 44,088 (45,221 ) Coal -- risk management 5,057 (31,397 ) 5,139 (9,892 ) Natural gas 24 (24 ) 27 — Total $ 50,216 $ (71,427 ) $ 54,608 $ (55,113 ) Total derivatives $ 50,526 $ (79,406 ) $ 55,550 $ (57,259 ) Effect of counterparty netting (42,851 ) 42,851 (50,042 ) 50,042 Net derivatives as classified in the balance sheets $ 7,675 $ (36,555 ) $ (28,880 ) $ 5,508 $ (7,217 ) $ (1,709 ) September 30, 2018 December 31, 2017 Net derivatives as reflected on the balance sheets (in thousands) Heating oil and coal Other current assets $ 7,675 $ 5,508 Coal Accrued expenses and other current liabilities (36,555 ) (7,217 ) $ (28,880 ) $ (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 $54.6 million and $16.2 million at September 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 September 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) $ (4,631 ) $ (169 ) $ (6,996 ) $ — Coal purchases (2) 424 152 2,171 — Totals $ (4,207 ) $ (17 ) $ (4,825 ) $ — 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 September 30, 2018 and 2017 . Derivatives Not Designated as Hedging Instruments (in thousands) Three Months Ended September 30, Gain (Loss) Recognized 2018 2017 Coal trading — realized and unrealized (3) $ (928 ) $ (696 ) Coal risk management — unrealized (3) (9,486 ) (212 ) Natural gas trading— realized and unrealized (3) (4 ) (120 ) Change in fair value of coal derivatives and coal trading activities, net total $ (10,418 ) $ (1,028 ) Coal risk management— realized (4) $ (2,537 ) $ — Heating oil — diesel purchases (4) $ 719 $ 822 ____________________________________________________________ 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) Nine Months Ended September 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) $ (14,862 ) $ 100 $ (6,996 ) $ — Coal purchases (2) 2,587 (82 ) 2,171 — Totals $ (12,275 ) $ 18 $ (4,825 ) $ — 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 nine month periods ended September 30, 2018 and 2017 . Derivatives Not Designated as Hedging Instruments (in thousands) Nine Months Ended September 30, Gain (Loss) Recognized 2018 2017 Coal trading — realized and unrealized (3) $ 14 $ (2,190 ) Coal risk management — unrealized (3) (22,116 ) (186 ) Natural gas trading— realized and unrealized (3) (40 ) (369 ) Change in fair value of coal derivatives and coal trading activities, net total $ (22,142 ) $ (2,745 ) Coal risk management— realized (4) $ (5,217 ) $ — Heating oil — diesel purchases (4) $ 4,394 $ (3,903 ) ____________________________________________________________ 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 September 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 $5.5 million .

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	9 Months Ended
Accrued Expenses and Other Current Liabilities	Sep. 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: September 30, December 31, 2018 2017 (In thousands) Payroll and employee benefits $ 48,961 $ 53,149 Taxes other than income taxes 72,095 77,017 Interest 237 246 Acquired sales contracts 562 934 Workers’ compensation 19,787 18,782 Asset retirement obligations 19,840 19,840 Coal derivative liability 36,555 7,217 Other 5,630 6,976 $ 203,667 $ 184,161

Debt and Financing Arrangements

Debt and Financing Arrangements	9 Months Ended
Debt and Financing Arrangements	Sep. 30, 2018
Debt Disclosure [Abstract]
Debt and Financing Arrangements	Debt and Financing Arrangements September 30, December 31, 2018 2017 (In thousands) Term loan due 2024 ($295.5 million face value) $ 294,327 $ 296,435 Other 26,338 36,514 Debt issuance costs (6,357 ) (7,032 ) 314,308 325,917 Less: current maturities of debt 11,478 15,783 Long-term debt $ 302,830 $ 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 August 27, 2018, 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 maintains the $160 million borrowing capacity and extends the maturity date to the date that is three years after the Securitization Facility Closing Date. Additionally, the amendment provided the Company the opportunity to use credit insurance to increase the pool of eligible receivables for borrowing. 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 364 th 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 September 30, 2018 , letters of credit totaling $75.0 million were outstanding under the facility which had a borrowing base of $83.3 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 September 30, 2018 , letters of credit totaling $35.7 million were outstanding under the facility with $4.3 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 September 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 September 30, 2018 is an asset of $3.6 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 $0.8 million of gains during the three and nine months ended September 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 $1.0 million of financing costs during the nine months ended September 30, 2018 ; $0.5 million related to the amendment of the Accounts Receivable Securitization Facility, with the remaining $0.5 million related to the Second Amendment to the Term Loan Facility. During the nine months ended September 30, 2017 , the Company paid $10.0 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 $2.4 million of legal and financial advisory fees associated with debt refinancing activities during the nine months ended September 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	9 Months Ended
Income Taxes	Sep. 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 September 30, Nine Months Ended September 30, 2018 2017 2018 2017 (In thousands) Income tax provision (benefit) at statutory rate $ 16,375 $ 23,347 $ 37,245 $ 54,843 Percentage depletion allowance (5,964 ) (7,708 ) (13,059 ) (20,439 ) State taxes, net of effect of federal taxes 4,528 728 5,865 1,619 Change in valuation allowance (44,278 ) (19,118 ) (62,234 ) (39,336 ) Current expense associated with uncertain tax positions 511 1,127 (599 ) 2,762 Impact of Tax Cut and Jobs Act of 2017 (19,780 ) — (19,780 ) — Other, net 3,393 (19 ) 3,437 67 Benefit from income taxes $ (45,215 ) $ (1,643 ) $ (49,125 ) $ (484 ) During the quarter, the IRS completed an audit of AMT NOL carryback claims the Company filed in prior periods. In addition, the Company filed an amended 2016 return which changed the amount of available tax attributes and the mix used to offset its bankruptcy cancellation of indebtedness income as of January 1, 2017. As a result, the Company increased available alternative minimum tax (“AMT”) credits and reduced other tax attributes as of that date that were available for attribute reduction. The AMT credits do not require a valuation allowance to be recorded against them due to the law changes enacted as part of the Tax Cut and Jobs Act of 2017 (the “Act”), while the Company’s other tax attributes are fully offset by a valuation allowance. The associated valuation allowance release related to the shift in attributes reflects what the Company believes will be realized upon audit of the amended return filing. The Company anticipates all AMT credits, net of sequestration, will be converted to cash in the next five years as provided by the Act. In total, these changes resulted in a recorded benefit from income taxes of $45.2 million , which was net of a $24.9 million uncertain tax position charge. On December 22, 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 AMT regime effective for tax years beginning after December 31, 2017, implementation of a process whereby corporations with unused AMT 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. During the quarter, the Company estimated the tax rate change impact of the Act on the 2016 amended return items. 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	9 Months Ended
Fair Value Measurements	Sep. 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 September 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: September 30, 2018 Total Level 1 Level 2 Level 3 (In thousands) Assets: Investments in marketable securities $ 162,530 $ 99,575 $ 62,955 $ — Derivatives 11,284 — 5,044 6,240 Total assets $ 173,814 $ 99,575 $ 67,999 $ 6,240 Liabilities: Derivatives $ 36,555 $ 34,838 $ 709 $ 1,008 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 September 30, 2018 Nine Months Ende d September 30, 2018 (In thousands) Balance, beginning of period $ 6,083 $ 5,426 Realized and unrealized gains recognized in earnings, net 749 4,402 Purchases 825 2,481 Issuances (70 ) (724 ) Settlements (2,355 ) (6,353 ) Ending balance $ 5,232 $ 5,232 Net unrealized gains of $0.8 million and $2.6 million were recognized in the Condensed Consolidated Income Statements within Other operating income, net during the three and nine months ended September 30, 2018 , respectively, related to Level 3 financial instruments held on September 30, 2018 . Fair Value of Long-Term Debt At September 30, 2018 and December 31, 2017 , the fair value of the Company’s debt, including amounts classified as current, was $322.6 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	9 Months Ended
Earnings per Common Share	Sep. 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 September 30, Nine Months Ended September 30, 2018 2017 2018 2017 (In thousands) Weighted average shares outstanding: Basic weighted average shares outstanding 19,250 23,580 20,102 24,416 Effect of dilutive securities 958 555 938 459 Diluted weighted average shares outstanding 20,208 24,135 21,040 24,875

Workers Compensation Expense

Workers Compensation Expense	9 Months Ended
Workers Compensation Expense	Sep. 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 September 30, Nine Months Ended September 30, 2018 2017 2018 2017 (In thousands) Self-insured occupational disease benefits: Service cost $ 1,860 $ 1,558 $ 5,580 $ 4,675 Interest cost (1) 1,196 1,169 3,585 3,506 Curtailments $ — $ (4,660 ) $ — $ (4,660 ) Total occupational disease $ 3,056 $ (1,933 ) $ 9,165 $ 3,521 Traumatic injury claims and assessments (2,069 ) 3,077 3,130 8,487 Total workers’ compensation expense $ 987 $ 1,144 $ 12,295 $ 12,008 During the third quarter of 2018, the Company recorded a $4.0 million reduction to its workers’ compensation liability with the offset to “Cost of Sales” in the Condensed Consolidated Income Statements. The liability was revalued using current claims data discounted at 3.08% . (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	9 Months Ended
Employee Benefit Plans	Sep. 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 September 30, Nine Months Ended September 30, 2018 2017 2018 2017 (In thousands) Interest cost (1) $ 2,376 $ 2,736 $ 6,917 $ 8,718 Expected return on plan assets (1) (2,906 ) (3,913 ) (9,067 ) (12,909 ) Pension settlement (1) (613 ) (229 ) (1,984 ) (716 ) Net benefit credit $ (1,143 ) $ (1,406 ) $ (4,134 ) $ (4,907 ) During the third 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 $3.3 million with the offset to accumulated other comprehensive income. The discount rate used for the revaluation was 4.17% . The following table details the components of other postretirement benefit costs: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 (In thousands) Service cost $ 140 $ 170 $ 419 $ 511 Interest cost (1) 918 1,058 2,755 3,175 Curtailments — (520 ) — (520 ) Net benefit cost $ 1,058 $ 708 $ 3,174 $ 3,166 (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	9 Months Ended
Commitments and Contingencies	Sep. 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 September 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	9 Months Ended
Segment Information	Sep. 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 the Company’s 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, 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 nine months ended September 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 September 30, 2018 Revenues $ 261,927 $ 236,328 $ 130,663 $ 4,262 $ 633,180 Adjusted EBITDA 48,646 81,250 25,200 (30,202 ) 124,894 Depreciation, depletion and amortization 9,114 18,106 3,924 631 31,775 Accretion on asset retirement obligation 4,885 469 565 1,073 6,992 Total assets 374,092 561,989 127,904 933,637 1,997,622 Capital expenditures 3,458 17,827 3,332 1,076 25,693 Three Months Ended September 30, 2017 Revenues $ 276,000 $ 238,946 $ 93,859 $ 4,733 $ 613,538 Adjusted EBITDA 48,768 53,346 21,217 (18,240 ) 105,091 Depreciation, depletion and amortization 9,577 18,479 3,465 393 31,914 Accretion on asset retirement obligation 5,040 511 540 1,489 7,580 Total assets 419,162 538,637 130,729 934,005 2,022,533 Capital expenditures 2,047 4,597 4,013 2,924 13,581 Nine Months Ende d September 30, 2018 Revenues $ 737,233 $ 733,707 $ 321,997 $ 7,887 $ 1,800,824 Adjusted EBITDA 102,639 251,649 52,710 (91,806 ) 315,192 Depreciation, depletion and amortization 25,841 53,109 11,459 1,618 92,027 Accretion on asset retirement obligation 14,656 1,406 1,696 3,219 20,977 Total assets 374,092 561,989 127,904 933,637 1,997,622 Capital expenditures 7,221 35,555 7,097 5,869 55,742 Nine Months Ended September 30, 2017 Revenues $ 780,007 $ 692,178 $ 287,404 $ 4,790 $ 1,764,379 Adjusted EBITDA 128,562 184,208 75,369 (66,229 ) 321,910 Depreciation, depletion and amortization 27,661 55,629 9,950 1,296 94,536 Accretion on asset retirement obligation 15,120 1,568 1,621 4,517 22,826 Total assets 419,162 538,637 130,729 934,005 2,022,533 Capital expenditures 2,997 16,032 6,653 4,821 30,503 A reconciliation of net income to adjusted EBITDA follows: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 (In thousands) Net income $ 123,192 $ 68,351 $ 226,483 $ 157,179 Benefit from income taxes (45,215 ) (1,643 ) (49,125 ) (484 ) Interest expense, net 3,378 5,252 10,998 19,311 Depreciation, depletion and amortization 31,775 31,914 92,027 94,536 Accretion on asset retirement obligations 6,992 7,580 20,977 22,826 Amortization of sales contracts, net 3,241 13,861 9,540 42,903 Gain on sale of Lone Mountain Processing, Inc. — (21,574 ) — (21,574 ) Net loss resulting from early retirement of debt and debt restructuring — 486 485 2,547 Non-service related pension and postretirement benefit costs 971 821 2,206 1,774 Reorganization items, net 560 43 1,601 2,892 Adjusted EBITDA $ 124,894 $ 105,091 $ 315,192 $ 321,910

Revenue Recognition

Revenue Recognition	9 Months Ended
Revenue Recognition	Sep. 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 September 30, 2018 North America revenues $ 261,927 $ 49,698 $ 56,051 $ 4,262 $ 371,938 Seaborne revenues — 186,630 74,612 — 261,242 Total revenues $ 261,927 $ 236,328 $ 130,663 $ 4,262 $ 633,180 Three Months Ended September 30, 2017 North America revenues $ 276,000 $ 84,411 $ 76,426 $ 4,733 $ 441,570 Seaborne revenues — 154,535 17,433 — 171,968 Total revenues $ 276,000 $ 238,946 $ 93,859 $ 4,733 $ 613,538 PRB MET Other Thermal Corporate, Other and Eliminations Consolidated (in thousands) Nine Months Ende d September 30, 2018 North America revenues $ 735,322 $ 117,699 $ 140,265 $ 7,887 $ 1,001,173 Seaborne revenues 1,911 616,008 181,732 — 799,651 Total revenues $ 737,233 $ 733,707 $ 321,997 $ 7,887 $ 1,800,824 Nine Months Ended September 30, 2017 North America revenues $ 780,007 $ 235,644 $ 216,929 $ 4,790 $ 1,237,370 Seaborne revenues — 456,534 70,475 — 527,009 Total revenues $ 780,007 $ 692,178 $ 287,404 $ 4,790 $ 1,764,379 As of September 30, 2018 , the Company has outstanding performance obligations for the remainder of 2018 of 18.5 million tons of fixed price contracts and 3.0 million tons of variable price contracts. Additionally, the Company has outstanding performance obligations beyond 2018 of approximately 80.4 million tons of fixed price contracts and 9.8 million tons of variable price contracts.

Basis of Presentation (Policies

Basis of Presentation (Policies)	9 Months Ended
Basis of Presentation (Policies)	Sep. 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 nine months ended September 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	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 19 , “ 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 nine months ended September 30, 2017 was adjusted to exclude the change in restricted cash as follows: (in thousands) Nine Months Ended September 30, 2017 Cash used in investing activities previously reported $ (29,603 ) Less: Withdrawals of restricted cash 71,048 Cash used in investing activities $ (100,651 ) 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 $1.0 million and $2.6 million reduction in cost of coal sales and a $0.2 million and $0.8 million increase in selling, general and administrative costs with the corresponding offset to Nonoperating expense for the three and nine months ended September 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. The Company expects 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 fourth quarter of 2018, although it does 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.

Accounting Policies (Tables)

Accounting Policies (Tables)	9 Months Ended
Accounting Policies (Tables)	Sep. 30, 2018
Accounting Policies [Abstract]
Schedule of net cash used in investing activities	As a result, net cash used in investing activities for the nine months ended September 30, 2017 was adjusted to exclude the change in restricted cash as follows: (in thousands) Nine Months Ended September 30, 2017 Cash used in investing activities previously reported $ (29,603 ) Less: Withdrawals of restricted cash 71,048 Cash used in investing activities $ (100,651 )

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Tables)	9 Months Ended
Accumulated Other Comprehensive Income (Tables)	Sep. 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) (9,743 ) 8,373 (355 ) (1,725 ) Amounts reclassified from AOCI 4,071 (1,984 ) (24 ) 2,063 Balance at September 30, 2018 $ (5,025 ) $ 26,109 $ (379 ) $ 20,705
Schedule of Comprehensive Income Reclassifications	The following amounts were reclassified out of AOCI: Three Months Ended September 30, Nine Months Ended September 30, Details About AOCI Components 2018 2017 2018 2017 Line Item in the Condensed Consolidated Statement of Operations (In thousands) Coal hedges $ (4,824 ) $ (88 ) $ (4,824 ) $ (88 ) Revenues Interest rate hedges 265 — 753 — Interest expense $ (4,559 ) $ (88 ) $ (4,071 ) $ (88 ) Net of tax Pension, postretirement and other post-employment benefits Pension settlement 613 228 1,984 715 Non-service related pension and postretirement benefit (costs) credits Actuarial curtailments — (773 ) — (773 ) Sale of Cumberland River Pension Plan — (360 ) — (360 ) $ 613 $ (905 ) $ 1,984 $ (418 ) Net of tax Available-for-sale securities $ 8 $ — $ 24 $ 332 Interest and investment income $ 8 $ — $ 24 $ 332 Net of tax

Inventories (Tables)

Inventories (Tables)	9 Months Ended
Inventories (Tables)	Sep. 30, 2018
Inventory Disclosure [Abstract]
Inventories	Inventories consist of the following: September 30, December 31, 2018 2017 (In thousands) Coal $ 77,497 $ 54,692 Repair parts and supplies 86,381 74,268 $ 163,878 $ 128,960

Investments in Available-for-_2

Investments in Available-for-Sale Securities (Tables)	9 Months Ended
Investments in Available-for-Sale Securities (Tables)	Sep. 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: September 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 $ 99,754 $ 1 $ (180 ) $ 99,575 $ 99,575 $ — Corporate notes and bonds 63,155 — (200 ) 62,955 62,955 — Total Investments $ 162,909 $ 1 $ (380 ) $ 162,530 $ 162,530 $ — 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)	9 Months Ended
Sales Contracts (Tables)	Sep. 30, 2018
Acquired Sales Contracts [Abstract]
Schedule of Sales Contracts	The sales contracts reflected in the Condensed Consolidated Balance Sheets are as follows: September 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 (95,104 ) (30,783 ) (84,760 ) (29,979 ) Total $ 2,092 $ 959 $ 1,133 $ 12,436 $ 1,763 $ 10,673 Balance Sheet classification: Other current $ 2,091 $ 562 $ 12,432 $ 934 Other noncurrent $ 1 $ 397 $ 4 $ 829

Derivatives (Tables)

Derivatives (Tables)	9 Months Ended
Derivatives (Tables)	Sep. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Price Risk Derivatives	At September 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 646 1,620 2,266 Coal purchases 284 118 402
Disclosure of Fair Value of Derivatives	The fair value and location of derivatives reflected in the accompanying Condensed Consolidated Balance Sheets are as follows: September 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 $ 310 $ (7,979 ) $ 942 $ (2,146 ) Derivatives Not Designated as Hedging Instruments Heating oil -- diesel purchases 6,240 — 5,354 — Coal -- held for trading purposes 38,895 (40,006 ) 44,088 (45,221 ) Coal -- risk management 5,057 (31,397 ) 5,139 (9,892 ) Natural gas 24 (24 ) 27 — Total $ 50,216 $ (71,427 ) $ 54,608 $ (55,113 ) Total derivatives $ 50,526 $ (79,406 ) $ 55,550 $ (57,259 ) Effect of counterparty netting (42,851 ) 42,851 (50,042 ) 50,042 Net derivatives as classified in the balance sheets $ 7,675 $ (36,555 ) $ (28,880 ) $ 5,508 $ (7,217 ) $ (1,709 ) September 30, 2018 December 31, 2017 Net derivatives as reflected on the balance sheets (in thousands) Heating oil and coal Other current assets $ 7,675 $ 5,508 Coal Accrued expenses and other current liabilities (36,555 ) (7,217 ) $ (28,880 ) $ (1,709 )
Effects of Derivatives on Measures of Financial Performance	The effects of derivatives on measures of financial performance are as follows: Derivatives used in Cash Flow Hedging Relationships (in thousands) Three Months Ended September 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) $ (4,631 ) $ (169 ) $ (6,996 ) $ — Coal purchases (2) 424 152 2,171 — Totals $ (4,207 ) $ (17 ) $ (4,825 ) $ — Derivatives Not Designated as Hedging Instruments (in thousands) Three Months Ended September 30, Gain (Loss) Recognized 2018 2017 Coal trading — realized and unrealized (3) $ (928 ) $ (696 ) Coal risk management — unrealized (3) (9,486 ) (212 ) Natural gas trading— realized and unrealized (3) (4 ) (120 ) Change in fair value of coal derivatives and coal trading activities, net total $ (10,418 ) $ (1,028 ) Coal risk management— realized (4) $ (2,537 ) $ — Heating oil — diesel purchases (4) $ 719 $ 822 ____________________________________________________________ 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) Nine Months Ended September 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) $ (14,862 ) $ 100 $ (6,996 ) $ — Coal purchases (2) 2,587 (82 ) 2,171 — Totals $ (12,275 ) $ 18 $ (4,825 ) $ — Derivatives Not Designated as Hedging Instruments (in thousands) Nine Months Ended September 30, Gain (Loss) Recognized 2018 2017 Coal trading — realized and unrealized (3) $ 14 $ (2,190 ) Coal risk management — unrealized (3) (22,116 ) (186 ) Natural gas trading— realized and unrealized (3) (40 ) (369 ) Change in fair value of coal derivatives and coal trading activities, net total $ (22,142 ) $ (2,745 ) Coal risk management— realized (4) $ (5,217 ) $ — Heating oil — diesel purchases (4) $ 4,394 $ (3,903 ) ____________________________________________________________ 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

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
Accrued Expenses and Other Current Liabilities (Tables)	Sep. 30, 2018
Payables and Accruals [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following: September 30, December 31, 2018 2017 (In thousands) Payroll and employee benefits $ 48,961 $ 53,149 Taxes other than income taxes 72,095 77,017 Interest 237 246 Acquired sales contracts 562 934 Workers’ compensation 19,787 18,782 Asset retirement obligations 19,840 19,840 Coal derivative liability 36,555 7,217 Other 5,630 6,976 $ 203,667 $ 184,161

Debt and Financing Arrangemen_2

Debt and Financing Arrangements (Tables)	9 Months Ended
Debt and Financing Arrangements (Tables)	Sep. 30, 2018
Debt Disclosure [Abstract]
Debt	September 30, December 31, 2018 2017 (In thousands) Term loan due 2024 ($295.5 million face value) $ 294,327 $ 296,435 Other 26,338 36,514 Debt issuance costs (6,357 ) (7,032 ) 314,308 325,917 Less: current maturities of debt 11,478 15,783 Long-term debt $ 302,830 $ 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 September 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)	9 Months Ended
Income Taxes (Tables)	Sep. 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 September 30, Nine Months Ended September 30, 2018 2017 2018 2017 (In thousands) Income tax provision (benefit) at statutory rate $ 16,375 $ 23,347 $ 37,245 $ 54,843 Percentage depletion allowance (5,964 ) (7,708 ) (13,059 ) (20,439 ) State taxes, net of effect of federal taxes 4,528 728 5,865 1,619 Change in valuation allowance (44,278 ) (19,118 ) (62,234 ) (39,336 ) Current expense associated with uncertain tax positions 511 1,127 (599 ) 2,762 Impact of Tax Cut and Jobs Act of 2017 (19,780 ) — (19,780 ) — Other, net 3,393 (19 ) 3,437 67 Benefit from income taxes $ (45,215 ) $ (1,643 ) $ (49,125 ) $ (484 )

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
Fair Value Measurements (Tables)	Sep. 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: September 30, 2018 Total Level 1 Level 2 Level 3 (In thousands) Assets: Investments in marketable securities $ 162,530 $ 99,575 $ 62,955 $ — Derivatives 11,284 — 5,044 6,240 Total assets $ 173,814 $ 99,575 $ 67,999 $ 6,240 Liabilities: Derivatives $ 36,555 $ 34,838 $ 709 $ 1,008
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 September 30, 2018 Nine Months Ende d September 30, 2018 (In thousands) Balance, beginning of period $ 6,083 $ 5,426 Realized and unrealized gains recognized in earnings, net 749 4,402 Purchases 825 2,481 Issuances (70 ) (724 ) Settlements (2,355 ) (6,353 ) Ending balance $ 5,232 $ 5,232

Earnings per Common Share (Tabl

Earnings per Common Share (Tables)	9 Months Ended
Earnings per Common Share (Tables)	Sep. 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 September 30, Nine Months Ended September 30, 2018 2017 2018 2017 (In thousands) Weighted average shares outstanding: Basic weighted average shares outstanding 19,250 23,580 20,102 24,416 Effect of dilutive securities 958 555 938 459 Diluted weighted average shares outstanding 20,208 24,135 21,040 24,875

Workers Compensation Expense (T

Workers Compensation Expense (Tables)	9 Months Ended
Workers Compensation Expense (Tables)	Sep. 30, 2018
Compensation Related Costs [Abstract]
Workers' compensation expense	Workers’ compensation expense consists of the following components: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 (In thousands) Self-insured occupational disease benefits: Service cost $ 1,860 $ 1,558 $ 5,580 $ 4,675 Interest cost (1) 1,196 1,169 3,585 3,506 Curtailments $ — $ (4,660 ) $ — $ (4,660 ) Total occupational disease $ 3,056 $ (1,933 ) $ 9,165 $ 3,521 Traumatic injury claims and assessments (2,069 ) 3,077 3,130 8,487 Total workers’ compensation expense $ 987 $ 1,144 $ 12,295 $ 12,008 During the third quarter of 2018, the Company recorded a $4.0 million reduction to its workers’ compensation liability with the offset to “Cost of Sales” in the Condensed Consolidated Income Statements. The liability was revalued using current claims data discounted at 3.08% . (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)	9 Months Ended
Employee Benefit Plans (Tables)	Sep. 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 September 30, Nine Months Ended September 30, 2018 2017 2018 2017 (In thousands) Service cost $ 140 $ 170 $ 419 $ 511 Interest cost (1) 918 1,058 2,755 3,175 Curtailments — (520 ) — (520 ) Net benefit cost $ 1,058 $ 708 $ 3,174 $ 3,166 (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 September 30, Nine Months Ended September 30, 2018 2017 2018 2017 (In thousands) Interest cost (1) $ 2,376 $ 2,736 $ 6,917 $ 8,718 Expected return on plan assets (1) (2,906 ) (3,913 ) (9,067 ) (12,909 ) Pension settlement (1) (613 ) (229 ) (1,984 ) (716 ) Net benefit credit $ (1,143 ) $ (1,406 ) $ (4,134 ) $ (4,907 )

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
Segment Information (Tables)	Sep. 30, 2018
Segment Reporting [Abstract]
Schedule of Operating Segment Results	PRB MET Other Thermal Corporate, Other and Eliminations Consolidated (in thousands) Three Months Ended September 30, 2018 Revenues $ 261,927 $ 236,328 $ 130,663 $ 4,262 $ 633,180 Adjusted EBITDA 48,646 81,250 25,200 (30,202 ) 124,894 Depreciation, depletion and amortization 9,114 18,106 3,924 631 31,775 Accretion on asset retirement obligation 4,885 469 565 1,073 6,992 Total assets 374,092 561,989 127,904 933,637 1,997,622 Capital expenditures 3,458 17,827 3,332 1,076 25,693 Three Months Ended September 30, 2017 Revenues $ 276,000 $ 238,946 $ 93,859 $ 4,733 $ 613,538 Adjusted EBITDA 48,768 53,346 21,217 (18,240 ) 105,091 Depreciation, depletion and amortization 9,577 18,479 3,465 393 31,914 Accretion on asset retirement obligation 5,040 511 540 1,489 7,580 Total assets 419,162 538,637 130,729 934,005 2,022,533 Capital expenditures 2,047 4,597 4,013 2,924 13,581 Nine Months Ende d September 30, 2018 Revenues $ 737,233 $ 733,707 $ 321,997 $ 7,887 $ 1,800,824 Adjusted EBITDA 102,639 251,649 52,710 (91,806 ) 315,192 Depreciation, depletion and amortization 25,841 53,109 11,459 1,618 92,027 Accretion on asset retirement obligation 14,656 1,406 1,696 3,219 20,977 Total assets 374,092 561,989 127,904 933,637 1,997,622 Capital expenditures 7,221 35,555 7,097 5,869 55,742 Nine Months Ended September 30, 2017 Revenues $ 780,007 $ 692,178 $ 287,404 $ 4,790 $ 1,764,379 Adjusted EBITDA 128,562 184,208 75,369 (66,229 ) 321,910 Depreciation, depletion and amortization 27,661 55,629 9,950 1,296 94,536 Accretion on asset retirement obligation 15,120 1,568 1,621 4,517 22,826 Total assets 419,162 538,637 130,729 934,005 2,022,533 Capital expenditures 2,997 16,032 6,653 4,821 30,503
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 September 30, Nine Months Ended September 30, 2018 2017 2018 2017 (In thousands) Net income $ 123,192 $ 68,351 $ 226,483 $ 157,179 Benefit from income taxes (45,215 ) (1,643 ) (49,125 ) (484 ) Interest expense, net 3,378 5,252 10,998 19,311 Depreciation, depletion and amortization 31,775 31,914 92,027 94,536 Accretion on asset retirement obligations 6,992 7,580 20,977 22,826 Amortization of sales contracts, net 3,241 13,861 9,540 42,903 Gain on sale of Lone Mountain Processing, Inc. — (21,574 ) — (21,574 ) Net loss resulting from early retirement of debt and debt restructuring — 486 485 2,547 Non-service related pension and postretirement benefit costs 971 821 2,206 1,774 Reorganization items, net 560 43 1,601 2,892 Adjusted EBITDA $ 124,894 $ 105,091 $ 315,192 $ 321,910

Revenue Recognition (Tables)

Revenue Recognition (Tables)	9 Months Ended
Revenue Recognition (Tables)	Sep. 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 September 30, 2018 North America revenues $ 261,927 $ 49,698 $ 56,051 $ 4,262 $ 371,938 Seaborne revenues — 186,630 74,612 — 261,242 Total revenues $ 261,927 $ 236,328 $ 130,663 $ 4,262 $ 633,180 Three Months Ended September 30, 2017 North America revenues $ 276,000 $ 84,411 $ 76,426 $ 4,733 $ 441,570 Seaborne revenues — 154,535 17,433 — 171,968 Total revenues $ 276,000 $ 238,946 $ 93,859 $ 4,733 $ 613,538 PRB MET Other Thermal Corporate, Other and Eliminations Consolidated (in thousands) Nine Months Ende d September 30, 2018 North America revenues $ 735,322 $ 117,699 $ 140,265 $ 7,887 $ 1,001,173 Seaborne revenues 1,911 616,008 181,732 — 799,651 Total revenues $ 737,233 $ 733,707 $ 321,997 $ 7,887 $ 1,800,824 Nine Months Ended September 30, 2017 North America revenues $ 780,007 $ 235,644 $ 216,929 $ 4,790 $ 1,237,370 Seaborne revenues — 456,534 70,475 — 527,009 Total revenues $ 780,007 $ 692,178 $ 287,404 $ 4,790 $ 1,764,379

Accounting Policies - Cash used

Accounting Policies - Cash used in investing activities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Condensed Cash Flow Statements, Captions [Line Items]
Cash used in investing activities			$ (64,266)	$ (100,651)
Cost of sales	$ 482,029	$ 494,379	1,411,197	1,389,294
Selling, general and administrative expenses	$ 22,909	21,290	$ 73,613	64,508
Accounting Standards Update 2016-08
Condensed Cash Flow Statements, Captions [Line Items]
Cost of sales		(1,000)		(2,600)
Selling, general and administrative expenses		$ 200		800
Cash used in investing activities previously reported
Condensed Cash Flow Statements, Captions [Line Items]
Cash used in investing activities				(29,603)
Withdrawals of restricted cash \| Accounting Standards Update 2016-08
Condensed Cash Flow Statements, Captions [Line Items]
Cash used in investing activities				$ 71,048

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Schedule of Accumulated Other Comprehensive Income (Loss)) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	$ 665,865
Unrealized gains (losses)	(1,725)
Amounts reclassified from AOCI	2,063
Ending Balance	687,140
Accumulated Other Comprehensive Income
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	20,367
Ending Balance	20,705
Derivative instruments
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	647
Unrealized gains (losses)	(9,743)
Amounts reclassified from AOCI	4,071
Ending Balance	(5,025)
Pension, postretirement and other post-employment benefits
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	19,720
Unrealized gains (losses)	8,373
Amounts reclassified from AOCI	(1,984)
Ending Balance	26,109
Available-for-sale securities
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	0
Unrealized gains (losses)	(355)
Amounts reclassified from AOCI	(24)
Ending Balance	$ (379)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Schedule of Reclassifications) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	$ 633,180	$ 613,538	$ 1,800,824	$ 1,764,379
Interest expense	(5,179)	(5,972)	(15,624)	(21,400)
Pension settlement	(971)	(821)	(2,206)	(1,774)
Interest and investment income	1,801	720	4,626	2,089
Net income	123,192	68,351	226,483	157,179
Reclassification out of Accumulated Other Comprehensive Income \| Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	(4,824)	(88)	(4,824)	(88)
Interest expense	265	0	753	0
Net income	(4,559)	(88)	(4,071)	(88)
Reclassification out of Accumulated Other Comprehensive Income \| Pension settlement
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension settlement	613	228	1,984	715
Reclassification out of Accumulated Other Comprehensive Income \| Actuarial curtailments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension settlement	0	(773)	0	(773)
Reclassification out of Accumulated Other Comprehensive Income \| Sale of Cumberland River Pension Plan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension settlement	0	(360)	0	(360)
Reclassification out of Accumulated Other Comprehensive Income \| Pension, postretirement and other post-employment benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net income	613	(905)	1,984	(418)
Reclassification out of Accumulated Other Comprehensive Income \| Available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and investment income	8	0	24	332
Net income	$ 8	$ 0	$ 24	$ 332

Divestitures (Narrative) (Detai

Divestitures (Narrative) (Details) $ in Thousands	Sep. 14, 2017USD ($)company	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of Lone Mountain Processing, Inc.		$ 0	$ 21,574	$ 0	$ 21,574
Discontinued operations, disposed of by sale \| Lone Mountain Processing LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of mining companies \| company	2
Net cash received in sale	$ 8,300
Proceeds offset by disbursements	1,300
Gain on sale of Lone Mountain Processing, Inc.	21,600
Defined benefit pension plan \| Discontinued operations, disposed of by sale \| Lone Mountain Processing LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Curtailments	4,700
Postretirement medical claims \| Discontinued operations, disposed of by sale \| Lone Mountain Processing LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Curtailments	$ 500

Reorganization items, net (Narr

Reorganization items, net (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Discontinued Operations and Disposal Groups [Abstract]
Reorganization items, net	$ (560)	$ (43)	$ (1,601)	$ (2,892)
Payments for reorganization items	$ 600	$ 200	$ 1,200	$ 4,800

Inventories (Details)

Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Coal	$ 77,497	$ 54,692
Repair parts and supplies	86,381	74,268
Inventories	163,878	128,960
Allowance for slow-moving and obsolete inventories	$ 1,000	$ 300

Investments in Available-for-_3

Investments in Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Cost Basis	$ 162,909	$ 156,189
Available-for-sale, Gains	1	22
Available-for-sale, Losses	(380)	(365)
Available-for-sale, Fair Value	162,530	155,846
Available-for-sale, Short-Term Investments	162,530	155,846
Short-term Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Short-Term Investments	162,530	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	99,754	64,151
Available-for-sale, Gains	1	22
Available-for-sale, Losses	(180)	(73)
Available-for-sale, Fair Value	99,575	64,100
U.S. government and agency securities \| Short-term Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Short-Term Investments	99,575	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	63,155	92,038
Available-for-sale, Gains	0	0
Available-for-sale, Losses	(200)	(292)
Available-for-sale, Fair Value	62,955	91,746
Corporate notes and bonds \| Short-term Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Short-Term Investments	62,955	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-_4

Investments in Available-for-Sale Securities (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Abstract]
Unrealized losses owned for less than 12 months	$ 151.6	$ 132

Sales Contracts (Schedule of Sa

Sales Contracts (Schedule of Sales Contracts) (Details) - USD ($) $ in Thousands	Sep. 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	(95,104)	(84,760)
Accumulated amortization, Liabilities	(30,783)	(29,979)
Total, Assets	2,092	12,436
Total, Liabilities	959	1,763
Net Total	1,133	10,673
Liabilities	562	934
Other current Assets
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Assets	2,091	12,432
Other Current Liabilities
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Liabilities	562	934
Other Noncurrent Assets
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Assets	1	4
Other Noncurrent Liabilities
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Liabilities	$ 397	$ 829

Derivatives (Narrative) (Detail

Derivatives (Narrative) (Details) gal in Millions, $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)$ / optiongal	Dec. 31, 2019USD ($)	Dec. 31, 2017USD ($)
Derivative [Line Items]
Current asset representing cash collateral posted \| $		$ 54.6		$ 16.2
Derivative contracts expected to be reclassified from OCI into earnings \| $		$ (5.5)
Not Designated as Hedging Instrument \| Heating Oil
Derivative [Line Items]
Percent of expected requirements covered		69.00%
Derivative, average price risk option strike price (in usd per gallon) \| $ / option		2.05
Not Designated as Hedging Instrument \| Diesel Purchases
Derivative [Line Items]
Percent of expected requirements covered		38.00%
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		48
Scenario, Forecast
Derivative [Line Items]
Value of trading portfolio realized - gains (losses) \| $	$ (0.4)		$ (0.7)

Derivatives (Schedule of Price

Derivatives (Schedule of Price Risk Derivatives) (Details) T in Thousands	9 Months Ended
	Sep. 30, 2018T
Coal sales
Derivative [Line Items]
Derivatives held (in tons)	2,266
Coal purchases
Derivative [Line Items]
Derivatives held (in tons)	402
2018 \| Coal sales
Derivative [Line Items]
Derivatives held (in tons)	646
2018 \| Coal purchases
Derivative [Line Items]
Derivatives held (in tons)	284
2019 \| Coal sales
Derivative [Line Items]
Derivatives held (in tons)	1,620
2019 \| Coal purchases
Derivative [Line Items]
Derivatives held (in tons)	118

Derivatives (Disclosure Of Fair

Derivatives (Disclosure Of Fair Value Of Derivatives) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative Assets	$ 50,526	$ 55,550
Derivative Liabilities	(79,406)	(57,259)
Effect of counterparty netting in derivative assets	(42,851)	(50,042)
Effect of counterparty netting in derivative liabilities	42,851	50,042
Derivative Asset	7,675	5,508
Derivative Liability	(36,555)	(7,217)
Net derivatives as classified in the balance sheets	(28,880)	(1,709)
Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative Assets	50,216	54,608
Derivative Liabilities	(71,427)	(55,113)
Not Designated as Hedging Instrument \| Coal Contract
Derivative [Line Items]
Derivative Assets	38,895	44,088
Derivative Liabilities	(40,006)	(45,221)
Coal Contract \| Designated as Hedging Instrument
Derivative [Line Items]
Derivative Assets	310	942
Derivative Liabilities	(7,979)	(2,146)
Coal Contract \| Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative Assets	5,057	5,139
Derivative Liabilities	(31,397)	(9,892)
Heating oil — diesel purchases \| Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative Assets	6,240	5,354
Derivative Liabilities	0	0
Natural gas \| Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative Assets	24	27
Derivative Liabilities	$ (24)	$ 0

Derivatives (Net Derivatives As

Derivatives (Net Derivatives As Reflected On The Balance Sheets) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Net derivatives as classified in the balance sheet	$ (28,880)	$ (1,709)
Accrued expenses and other current liabilities
Derivatives, Fair Value [Line Items]
Net derivatives as classified in the balance sheet	(36,555)	(7,217)
Heating oil and coal \| Other current assets
Derivatives, Fair Value [Line Items]
Net derivatives as classified in the balance sheet	$ 7,675	$ 5,508

Derivatives (Effects Of Derivat

Derivatives (Effects Of Derivatives On Measures Of Financial Performance) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Change in fair value of coal derivatives and coal trading activities, net	$ (10,418)	$ (1,028)	$ (22,142)	$ (2,745)
Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income (Effective Portion)	(4,207)	(17)	(12,275)	18
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion)	(4,825)		(4,825)
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)	(4,631)	(169)	(14,862)	100
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion)	(6,996)	0	(6,996)	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)	424	152	2,587	(82)
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion)	2,171		2,171
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	(928)	(696)	14	(2,190)
Unrealized Gain (Loss) on Derivatives	(9,486)	(212)	(22,116)	(186)
Not Designated as Hedging Instrument \| Coal Contract \| Other operating (income) expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gain (Loss) on Derivatives	(2,537)	0	(5,217)	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	(4)	(120)	(40)	(369)
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	$ 719	$ 822	$ 4,394	$ (3,903)

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Payroll and employee benefits	$ 48,961	$ 53,149
Taxes other than income taxes	72,095	77,017
Interest	237	246
Acquired sales contracts	562	934
Workers’ compensation	19,787	18,782
Asset retirement obligations	19,840	19,840
Coal derivative liability	36,555	7,217
Other	5,630	6,976
Accrued expenses and other current liabilities	$ 203,667	$ 184,161

Debt and Financing Arrangemen_3

Debt and Financing Arrangements (Long term Debt) (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Other	$ 26,338,000	$ 36,514,000
Debt issuance costs	(6,357,000)	(7,032,000)
Total	314,308,000	325,917,000
Less: current maturities of debt	11,478,000	15,783,000
Long-term debt	302,830,000	310,134,000
Term loan due 2024 ($295.5 million face value)
Debt Instrument [Line Items]
Term loan	294,327,000	$ 296,435,000
Debt instrument, face amount	$ 295,500,000

Debt and Financing Arrangemen_4

Debt and Financing Arrangements (Narrative) (Details) - USD ($)	Aug. 27, 2018	Apr. 27, 2018	Apr. 03, 2018	Sep. 25, 2017	Apr. 27, 2017	Mar. 07, 2017	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Line of Credit Facility [Line Items]
Fair value of derivative assets							$ 50,526,000	$ 50,526,000		$ 55,550,000
Debt financing costs								1,009,000	$ 10,043,000
Debt restructuring costs								50,000	$ 2,360,000
Interest Rate Swap
Line of Credit Facility [Line Items]
Interest rate swaps settlements gains							300,000	800,000
Other Noncurrent Assets \| Interest Rate Swap
Line of Credit Facility [Line Items]
Fair value of derivative assets							$ 3,600,000	3,600,000
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%
Call premium rate			1.00%
Basis spread on variable rate, floor			1.00%
Senior Notes \| New Term Loan Debt Facility \| Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate			1.75%
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]
Debt financing costs								500,000
Line of Credit \| Secured Debt \| Accounts Receivable Securitization Facility \| Arch Receivable Company, LLC
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 160,000,000
Maturity date	3 years	3 years
Current borrowing capacity							$ 83,300,000	83,300,000
Covenant minimum amount					$ 175,000,000
Liquidity threshold, consecutive days		60 days
Liquidity threshold		364 days
Liquidity threshold, expiration period		60 days
Letters of credit outstanding							75,000,000	75,000,000
Line of Credit \| Secured Debt \| Inventory-Based Revolving Credit Facility \| Regions Bank
Line of Credit Facility [Line Items]
Debt instrument, face amount					40,000,000
Covenant minimum amount					$ 175,000,000
Liquidity threshold, consecutive days		60 days
Liquidity threshold		364 days
Liquidity threshold, expiration period		60 days
Letters of credit outstanding							35,700,000	35,700,000
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							$ 4,300,000	$ 4,300,000
Line of Credit \| Secured Debt \| Inventory-Based Revolving Credit Facility \| LIBOR \| Regions Bank \| Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate					2.25%
Line of Credit \| Secured Debt \| Inventory-Based Revolving Credit Facility \| LIBOR \| Regions Bank \| Maximum
Line of Credit Facility [Line Items]
Percentage of clause borrowing base					2.50%
Line of Credit \| Secured Debt \| Inventory-Based Revolving Credit Facility \| Base Rate \| Regions Bank \| Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate					1.25%
Line of Credit \| Secured Debt \| Inventory-Based Revolving Credit Facility \| Base Rate \| Regions Bank \| Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate					1.50%

Debt and Financing Arrangemen_5

Debt and Financing Arrangements (Interest rate derivatives) (Details) $ in Millions	Sep. 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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income tax provision (benefit) at statutory rate	$ 16,375	$ 23,347	$ 37,245	$ 54,843
Percentage depletion allowance	(5,964)	(7,708)	(13,059)	(20,439)
State taxes, net of effect of federal taxes	4,528	728	5,865	1,619
Change in valuation allowance	(44,278)	(19,118)	(62,234)	(39,336)
Current expense associated with uncertain tax positions	511	1,127	(599)	2,762
Impact of Tax Cut and Jobs Act of 2017	(19,780)	0	(19,780)	0
Other, net	3,393	(19)	3,437	67
Benefit from income taxes	45,215	$ 1,643	$ 49,125	$ 484
Uncertain tax position charge	$ 24,900

Fair Value Measurements (Summar

Fair Value Measurements (Summary Of Financial Assets And Liabilities Accounted For At Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets:
Investments in marketable securities	$ 162,530	$ 155,846
Derivatives	11,284
Total assets	173,814
Liabilities:
Derivatives	36,555	$ 7,217
Level 1
Assets:
Investments in marketable securities	99,575
Derivatives	0
Total assets	99,575
Liabilities:
Derivatives	34,838
Level 2
Assets:
Investments in marketable securities	62,955
Derivatives	5,044
Total assets	67,999
Liabilities:
Derivatives	709
Level 3
Assets:
Investments in marketable securities	0
Derivatives	6,240
Total assets	6,240
Liabilities:
Derivatives	$ 1,008

Fair Value Measurements (Summ_2

Fair Value Measurements (Summary Of Change In The Fair Values Of Financial Instruments Categorized As Level 3) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	$ 6,083	$ 5,426
Realized and unrealized gains recognized in earnings, net	749	4,402
Purchases	825	2,481
Issuances	(70)	(724)
Settlements	(2,355)	(6,353)
Ending balance	$ 5,232	$ 5,232

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 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	$ 322.6	$ 322.6	$ 336.1
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net unrealized gains (losses) related to level 3 financial instruments	$ 0.8	$ 2.6

Earnings per Common Share (Weig

Earnings per Common Share (Weighted-Average Number of Shares) (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Weighted average shares outstanding:
Basic weighted average shares outstanding (in shares)	19,250	23,580	20,102	24,416
Effect of dilutive securities (in shares)	958	555	938	459
Diluted weighted average shares outstanding (in shares)	20,208	24,135	21,040	24,875

Workers Compensation Expense (D

Workers Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accrued Workers Compensation [Line Items]
Reduction to workers' compensation liability	$ 4,000		$ 4,000
Data discount rate	3.08%
Occupational disease
Accrued Workers Compensation [Line Items]
Service cost	$ 1,860	$ 1,558	5,580	$ 4,675
Interest cost	1,196	1,169	3,585	3,506
Curtailments	0	(4,660)	0	(4,660)
Net benefit credit	3,056	(1,933)	9,165	3,521
Traumatic injury claims and assessments
Accrued Workers Compensation [Line Items]
Traumatic injury claims and assessments	(2,069)	3,077	3,130	8,487
Total workers’ compensation expense
Accrued Workers Compensation [Line Items]
Total workers’ compensation expense	$ 987	$ 1,144	$ 12,295	$ 12,008

Employee Benefit Plans (Pension

Employee Benefit Plans (Pension And Other Postretirement Benefit Costs) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined benefit pension plan
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 2,376	$ 2,736	$ 6,917	$ 8,718
Expected return on plan assets	(2,906)	(3,913)	(9,067)	(12,909)
Pension settlement	(613)	(229)	(1,984)	(716)
Net benefit credit	(1,143)	(1,406)	(4,134)	(4,907)
Other postretirement benefits plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	140	170	419	511
Interest cost	918	1,058	2,755	3,175
Curtailments	0	(520)	0	(520)
Net benefit credit	$ 1,058	$ 708	$ 3,174	$ 3,166

Employee Benefit Plans (Narrati

Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Decrease in defined benefit plan obligation	$ 105,400	$ 102,369
Defined benefit pension plan
Defined Benefit Plan Disclosure [Line Items]
Cash balance revaluation discount rate	4.17%
Change in assumptions for defined benefit plans \| Defined benefit pension plan
Defined Benefit Plan Disclosure [Line Items]
Decrease in defined benefit plan obligation	$ 3,300

Commitments and Contingencies (

Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions	Sep. 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		9 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)Segment	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Segment Reporting [Abstract]
Number of reportable segments \| Segment			2
Segment Reporting Information [Line Items]
Revenues	$ 633,180	$ 613,538	$ 1,800,824	$ 1,764,379
Adjusted EBITDA	124,894	105,091	315,192	321,910
Depreciation, depletion and amortization	31,775	31,914	92,027	94,536
Accretion on asset retirement obligations	6,992	7,580	20,977	22,826
Total assets	1,997,622	2,022,533	1,997,622	2,022,533	$ 1,979,632
Capital expenditures	25,693	13,581	55,742	30,503
Operating Segments \| PRB
Segment Reporting Information [Line Items]
Revenues	261,927	276,000	737,233	780,007
Adjusted EBITDA	48,646	48,768	102,639	128,562
Depreciation, depletion and amortization	9,114	9,577	25,841	27,661
Accretion on asset retirement obligations	4,885	5,040	14,656	15,120
Total assets	374,092	419,162	374,092	419,162
Capital expenditures	3,458	2,047	7,221	2,997
Operating Segments \| MET
Segment Reporting Information [Line Items]
Revenues	236,328	238,946	733,707	692,178
Adjusted EBITDA	81,250	53,346	251,649	184,208
Depreciation, depletion and amortization	18,106	18,479	53,109	55,629
Accretion on asset retirement obligations	469	511	1,406	1,568
Total assets	561,989	538,637	561,989	538,637
Capital expenditures	17,827	4,597	35,555	16,032
Operating Segments \| Other Thermal
Segment Reporting Information [Line Items]
Revenues	130,663	93,859	321,997	287,404
Adjusted EBITDA	25,200	21,217	52,710	75,369
Depreciation, depletion and amortization	3,924	3,465	11,459	9,950
Accretion on asset retirement obligations	565	540	1,696	1,621
Total assets	127,904	130,729	127,904	130,729
Capital expenditures	3,332	4,013	7,097	6,653
Corporate, Other and Eliminations
Segment Reporting Information [Line Items]
Revenues	4,262	4,733	7,887	4,790
Adjusted EBITDA	(30,202)	(18,240)	(91,806)	(66,229)
Depreciation, depletion and amortization	631	393	1,618	1,296
Accretion on asset retirement obligations	1,073	1,489	3,219	4,517
Total assets	933,637	934,005	933,637	934,005
Capital expenditures	$ 1,076	$ 2,924	$ 5,869	$ 4,821

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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting [Abstract]
Net income	$ 123,192	$ 68,351	$ 226,483	$ 157,179
Benefit from income taxes	(45,215)	(1,643)	(49,125)	(484)
Interest expense, net	3,378	5,252	10,998	19,311
Depreciation, depletion and amortization	31,775	31,914	92,027	94,536
Accretion on asset retirement obligations	6,992	7,580	20,977	22,826
Amortization of sales contracts, net	3,241	13,861	9,540	42,903
Gain on sale of Lone Mountain Processing, Inc.	0	(21,574)	0	(21,574)
Net loss resulting from early retirement of debt and debt restructuring	0	486	485	2,547
Non-service related pension and postretirement benefit costs	971	821	2,206	1,774
Reorganization items, net	560	43	1,601	2,892
Adjusted EBITDA	$ 124,894	$ 105,091	$ 315,192	$ 321,910

Revenue Recognition (Details)

Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Revenue Recognition (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 633,180	$ 613,538	$ 1,800,824	$ 1,764,379
Corporate, Other and Eliminations
Disaggregation of Revenue [Line Items]
Revenues	4,262	4,733	7,887	4,790
North America revenues
Disaggregation of Revenue [Line Items]
Revenues	371,938	441,570	1,001,173	1,237,370
North America revenues \| Corporate, Other and Eliminations
Disaggregation of Revenue [Line Items]
Revenues	4,262	4,733	7,887	4,790
Seaborne revenues
Disaggregation of Revenue [Line Items]
Revenues	261,242	171,968	799,651	527,009
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	261,927	276,000	737,233	780,007
PRB \| North America revenues \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	261,927	276,000	735,322	780,007
PRB \| Seaborne revenues \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0	0	1,911	0
MET \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	236,328	238,946	733,707	692,178
MET \| North America revenues \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	49,698	84,411	117,699	235,644
MET \| Seaborne revenues \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	186,630	154,535	616,008	456,534
Other Thermal \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	130,663	93,859	321,997	287,404
Other Thermal \| North America revenues \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	56,051	76,426	140,265	216,929
Other Thermal \| Seaborne revenues \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	$ 74,612	$ 17,433	$ 181,732	$ 70,475

Revenue Recognition (Narrative)

Revenue Recognition (Narrative) (Details) T in Millions	Sep. 30, 2018T
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations, fixed price contracts (in tons)	18.5
Remaining performance obligations, variable price contracts (in tons)	3
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations, fixed price contracts (in tons)	80.4
Remaining performance obligations, variable price contracts (in tons)	9.8