Arch Resources (ARCH) 10-K 28 Feb 14 2013 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013	Feb. 13, 2014	Jun. 30, 2013
Document and Entity Information [Abstract]	'	'	'
Entity Registrant Name	'ARCH COAL INC	'	'
Entity Central Index Key	'0001037676	'	'
Document Type	'10-K	'	'
Document Period End Date	31-Dec-13	'	'
Amendment Flag	'false	'	'
Current Fiscal Year End Date	'--12-31	'	'
Document Fiscal Year Focus	'2013	'	'
Document Fiscal Period Focus	'FY	'	'
Entity Filer Category	'Large Accelerated Filer	'	'
Entity Common Stock, Shares Outstanding	'	212,279,999	'
Entity Well known seasoned issuer	'Yes	'	'
Entity Voluntary Filers	'No	'	'
Entity Current reporting status	'Yes	'	'
Entity Public Float	'	'	$791.10

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement [Abstract]	'	'	'
Revenues	$3,014,357	$3,768,126	$3,883,039
Costs, expenses and other operating	'	'	'
Cost of sales (exclusive of items shown separately below)	2,663,136	3,155,099	2,980,354
Depreciation, depletion and amortization	426,442	492,211	420,980
Amortization of acquired sales contracts, net	-9,457	-25,189	-22,069
Sales contract amortization	-9,457	-25,189	-22,069
Change in fair value of coal derivatives and coal trading activities, net	7,845	-16,590	-2,907
Coal derivative settlements, non-hedging	-32,534	-43,990	7
Asset impairment and mine closure costs	220,879	539,182	7,316
Goodwill, Impairment Loss	265,423	330,680	0
Contract settlement resulting from Patriot Coal bankruptcy	0	58,335	0
Reduction in accrual related to acquired litigation	'	79,532	0
Acquisition and transition costs	0	0	47,360
Selling, general and administrative expenses	133,448	134,299	119,056
Other operating expense (income), net	2,316	-19,367	-10,119
Total operating expenses	3,677,498	4,525,138	3,539,978
Income from investment in subsidiaries	'	'	'
Income (loss) from operations	-663,141	-757,012	343,061
Interest expense, net	'	'	'
Interest expense	-381,267	-317,615	-230,186
Interest and investment income	6,603	5,473	3,309
Interest Income (Expense), Nonoperating, Net	-374,664	-312,142	-226,877
Nonoperating expense	'	'	'
Net loss resulting from early retirement and refinancing of debt	-42,921	-23,668	-1,958
Debt Related Commitment Fees and Debt Issuance Costs	0	0	-49,490
Nonoperating expense, net	-42,921	-23,668	-51,448
Loss from continuing operations before income taxes	-1,080,726	-1,092,822	64,736
Benefit from income taxes	-335,498	-353,907	-24,279
Income (loss) from continuing operations	-745,228	-738,915	89,015
Income from discontinued operations, including gain on sale - net of tax	103,396	55,228	53,825
Net income (loss)	-641,832	-683,687	142,840
Less: Net income attributable to noncontrolling interest	'	-268	-1,157
Net income (loss) attributable to Arch Coal, Inc.	-641,832	-683,955	141,683
Earnings (loss) per common share	'	'	'
Income (Loss) from Continuing Operations, Per Basic Share	($3.52)	($3.50)	$0.47
Income (Loss) from Continuing Operations, Per Diluted Share	($3.52)	($3.50)	$0.47
Basic earnings (loss) per common share	($3.03)	($3.24)	$0.75
Diluted earnings (loss) per common share	($3.03)	($3.24)	$0.74
Weighted average shares outstanding	'	'	'
Basic, weighted average shares outstanding	212,098	211,381	190,086
Diluted, weighted average shares outstanding	212,098	211,381	190,905
Dividends declared per common share	$0.12	$0.20	$0.43
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	($587,633)	($692,239)	$141,240

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Current assets	'	'
Cash and cash equivalents	$911,099	$784,622
Restricted cash	'	3,453
Short term investments	248,414	234,305
Trade accounts receivable	198,020	247,539
Other receivables	31,553	84,541
Inventories	264,161	365,424
Prepaid royalties	8,083	11,416
Deferred income taxes	49,144	67,360
Other current assets	56,746	92,469
Total current assets	1,782,071	1,914,104
Property, plant and equipment	'	'
Coal lands and mineral rights	5,991,719	6,218,776
Plant and equipment	2,882,486	3,391,265
Deferred mine development	979,270	1,079,856
Property, Plant and Equipment, Gross	9,853,475	10,689,897
Less accumulated depreciation, depletion and amortization	-3,119,189	-3,352,799
Property, plant and equipment, net	6,734,286	7,337,098
Other assets	'	'
Prepaid royalties	87,577	87,773
Goodwill	0	265,423
Equity investments	221,456	242,215
Other noncurrent assets	164,803	160,164
Total other assets	473,836	755,575
Total assets	8,990,193	10,006,777
Current liabilities	'	'
Accounts payable	176,142	224,418
Accrued expenses and other current liabilities	278,575	318,018
Current maturities of debt	33,493	32,896
Total current liabilities	488,222	577,069
Long-term debt	5,118,002	5,085,879
Asset retirement obligations	402,713	409,705
Accrued pension benefits	7,111	67,630
Accrued postretirement benefits other than pension	39,255	45,086
Accrued workers’ compensation	78,062	81,629
Deferred income taxes	413,546	664,182
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent	-413,546	-664,182
Other noncurrent liabilities	190,033	221,030
Total liabilities	6,736,944	7,152,210
Stockholders' equity	'	'
Common stock, $0.01 par value, authorized 260,000 shares, issued 213,792 and 213,759 shares at December 31, 2013 and December 31, 2012, respectively	2,141	2,141
Paid-in capital	3,038,613	3,026,823
Treasury stock, at cost	-53,848	-53,848
Accumulated deficit	-771,349	-104,042
Accumulated other comprehensive income (loss)	37,692	-16,507
Total stockholders’ equity	2,253,249	2,854,567
Total liabilities and stockholders’ equity	8,990,193	10,006,777
Coal Contract [Member]	'	'
Current assets	'	'
Coal derivative assets	14,851	22,975
Current liabilities	'	'
Coal derivative assets	$12	$1,737

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (Loss) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Other Comprehensive Income (Loss), Net of Tax [Abstract]	'	'	'
Net income (loss)	($641,832)	($683,687)	$142,840
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax	-2,626	10,894	-11,953
Derivatives Qualifying as Hedges, Tax benefit	947	-3,921	4,303
Derivatives Qualifying as Hedges, Adjustment, Net of Tax	-1,679	6,973	-7,650
Pension and Other Postretirement Benefit Plans, Total comprehensive income (loss) before tax	77,201	-21,291	9,376
Pension and Other Postretirement Benefit Plans, Tax impact	-27,803	7,686	-3,440
Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	49,398	-13,605	5,936
Available-for-sale Securities Adjustment, Total comprehensive income (loss) before tax	10,190	-3,000	114
Available-for-sale Securities, Tax benefit	-3,710	1,080	0
Available-for-sale Securities Adjustment, Net of Tax	6,480	-1,920	114
Total other comprehensive income (loss)	54,199	-8,552	-1,600
Total comprehensive income (loss)	($587,633)	($692,239)	$141,240

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]	'	'
Common stock, par value	$0.01	$0.01
Common stock, shares authorized	260,000,000	260,000,000
Common stock, shares issued	213,791,799	213,759,000

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating activties	'	'	'
Net income (loss)	($641,832)	($683,687)	$142,840
Adjustments to reconcile net loss to cash provided by operating activities:	'	'	'
Depreciation, depletion and amortization	447,704	525,508	466,587
Amortization of acquired sales contracts, net	-9,457	-25,189	-22,069
Sales contract amortization	-9,457	-25,189	-22,069
Amortization relating to financing activities	24,789	20,238	14,067
Prepaid royalties expensed	13,706	22,650	34,842
Employee stock-based compensation expense	11,790	11,822	10,882
Net loss resulting from early retirement of debt and financing activities	-42,921	-23,668	-51,448
Amortization of premiums on debt securities held	3,680	'	'
Gain on sale of Canyon Fuel	-120,321	0	0
Asset impairment and mine closure costs	220,879	539,182	7,316
Payments for Restructuring	'	531,234	'
Goodwill impairment	265,423	330,680	0
Changes in:	'	'	'
Receivables	62,881	113,531	-74,914
Inventories	44,635	9,468	-50,900
Accounts payable, accrued expenses and other current liabilities	-77,521	-171,580	52,191
Income taxes, net	-4,520	27,545	-21,759
Deferred income taxes	-263,099	-336,036	10,519
Asset retirement obligations	17,432	-42,531	3,868
Other	13,046	-11,359	11,245
Cash provided by operating activities	55,742	332,804	642,242
Investing activities	'	'	'
Capital expenditures	-296,984	-395,225	-540,936
Acquisition of businesses, net of cash acquired	'	0	-2,894,339
Additions to prepaid royalties	-14,947	-13,269	-29,957
Proceeds from dispositions of property, plant and equipment	10,790	22,825	25,887
Proceeds from sale-leaseback transactions	34,919	'	'
Proceeds from sale of Canyon Fuel	422,663	'	'
Purchases of short term investments	213,726	236,862	0
Proceeds from sales of short term investments	194,537	1,754	0
Investments in and advances to affiliates	-15,260	-17,758	-61,909
Purchase of noncontrolling interest	0	'	0
Change in restricted cash	3,453	6,869	5,167
Consideration paid related to prior business acquisitions	'	0	-829
Cash provided by (used in) investing activities	125,445	-649,166	-3,496,916
Financing activities	'	'	'
Proceeds from Issuance of Secured Debt	294,000	1,633,500	'
Proceeds from issuance of senior notes	350,000	359,753	2,000,000
Proceeds from the issuance of common stock, net	'	0	1,267,933
Payments to retire debt	-629,172	-452,934	-605,178
Payments on term loan	-17,250	-7,625	'
Net decrease in borrowings under lines of credit	'	-481,300	424,396
Net payments on other debt	-6,324	-682	5,334
Debt financing costs	-20,489	-50,568	-114,823
Dividends paid	-25,475	-42,440	-80,748
Proceeds from exercise of options under incentive plans	'	5,131	2,316
Cash provided by (used in) financing activities	-54,710	962,835	2,899,230
Increase in cash and cash equivalents	126,477	646,473	44,556
Cash and cash equivalents, beginning of period	784,622	138,149	93,593
Cash and cash equivalents, end of period	911,099	784,622	138,149
SUPPLEMENTAL CASH FLOW INFORMATION	'	'	'
Cash paid during the year for interest	380,389	310,241	213,697
Cash paid (refunded) during the year for income taxes, net	-18,741	-28,057	7,094
Coal Contract [Member]	'	'	'
Changes in:	'	'	'
Coal derivative assets and liabilities	$3,606	($13,158)	$6,079

Consolidated_Statements_of_Sto

Consolidated Statements of Stockholders' Equity (USD $)	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
In Thousands, unless otherwise specified
Beginning Balance at Dec. 31, 2010	$2,237,507	$1,645	$1,734,709	($53,848)	$561,418	($6,417)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]	'	'	'	'	'	'
Net income attributable to Arch Coal, Inc.	141,683	'	'	'	141,683	'
Total comprehensive income (loss)	140,150	'	'	'	'	-1,533
Dividends, Common Stock	-80,748	'	'	'	-80,748	'
Dividends on common shares	80,748	'	'	'	'	'
Redemption of noncontrolling interest	1,267,933	487	1,267,446	'	'	'
Issuance of shares of common stock under the stock incentive plan — restricted stock and restricted stock units, net of forfeitures	'	2	-2	'	'	'
Issuance of shares of common stock under the stock incentive plan — stock options including income tax benefits	2,316	2	2,314	'	'	'
Employee stock-based compensation expense	10,882	'	10,882	'	'	'
Employee stock-based compensation expense	10,882	'	'	'	'	'
Ending Balance at Dec. 31, 2011	3,578,040	2,136	3,015,349	-53,848	622,353	-7,950
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]	'	'	'	'	'	'
Net income attributable to Arch Coal, Inc.	-683,955	'	'	'	-683,955	'
Total comprehensive income (loss)	-692,512	'	'	'	'	-8,557
Dividends, Common Stock	-42,440	'	'	'	-42,440	'
Dividends on common shares	42,440	'	'	'	'	'
Redemption of noncontrolling interest	'	'	-5,474	'	'	'
Redemption of noncontrolling interest	-5,474	'	'	'	'	'
Issuance of shares of common stock under the stock incentive plan — restricted stock and restricted stock units, net of forfeitures	0	0	0	'	'	'
Issuance of shares of common stock under the stock incentive plan — stock options including income tax benefits	5,131	5	5,126	'	'	'
Employee stock-based compensation expense	11,822	'	11,822	'	'	'
Employee stock-based compensation expense	11,822	'	'	'	'	'
Ending Balance at Dec. 31, 2012	2,854,567	2,141	3,026,823	-53,848	-104,042	-16,507
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]	'	'	'	'	'	'
Net income attributable to Arch Coal, Inc.	-641,832	'	'	'	'	'
Total comprehensive income (loss)	-587,633	'	'	'	'	54,199
Dividends, Common Stock	'	'	'	'	-25,475	'
Dividends on common shares	25,475	'	'	'	'	'
Issuance of shares of common stock under the stock incentive plan — restricted stock and restricted stock units, net of forfeitures	0	0	0	'	'	'
Employee stock-based compensation expense	11,790	'	'	'	'	'
Employee stock-based compensation expense	11,790	'	'	'	'	'
Ending Balance at Dec. 31, 2013	$2,253,249	$2,141	$3,038,613	($53,848)	($771,349)	$37,692

Consolidated_Statements_of_Sto1

Consolidated Statements of Stockholders' Equity (Parenthetical)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement of Stockholders' Equity [Abstract]	'	'	'
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures	39	49	162
Stock Issued During Period, Value, Stock Options Exercised	-6	526	199
Common stock issued	'	'	48,705

Basis_of_Presentation

Basis of Presentation	12 Months Ended
	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block]	'
	Basis of Presentation
	The accompanying consolidated financial statements include the accounts of Arch Coal, Inc. and its subsidiaries and controlled entities (the “Company”). 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, Kentucky, Maryland, Virginia, Illinois, Wyoming and Colorado. All subsidiaries are wholly-owned. Intercompany transactions and accounts have been eliminated in consolidation.
	The Company completed the sale of Canyon Fuel Company, LLC (Canyon Fuel) on August 16, 2013. The results of these mining complexes have been segregated from continuing operations and are reflected, net of tax, as discontinued operations in the consolidated statements of operations for all periods presented. See further discussion in Note 3, "Discontinued Operations".
	In response to decreasing demand for thermal coal in Appalachia, the Company closed four mining complexes, temporarily idled a fifth complex, and curtailed production at other mines in the Appalachia region in the second quarter of 2012. The results for the closed and idled complexes are reflected in income from continuing operations in the consolidated statements of operations. See further discussion in Note 5, "Impairment Charges and Mine Closure Costs".
	The Company's subsidiary Arch Western Resources, LLC (“Arch Western”) operates thermal coal mines in the western U.S. On April 9, 2012, Delta Housing, Inc., a subsidiary of BP p.l.c. and a joint venture partner in Arch Western, exercised their contractual right to require the Company to purchase their common and preferred membership interests in Arch Western.  With the payment of the negotiated purchase amount of $17.5 million on July 2, 2012, Arch Western became a wholly-owned subsidiary.

Accounting_Policies

Accounting Policies	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Accounting Policies	'
	Accounting Policies
	The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States for financial reporting and U.S. Securities and Exchange Commission regulations.
	Accounting Pronouncements
	There are no accounting pronouncements whose adoption had, or is expected to have, a material impact on the Company's consolidated financial statements.
	Accounting Estimates
	The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and revenues and expenses in the accompanying consolidated financial statements and the disclosure of contingent assets and liabilities. Actual results could differ from those estimates.
	Cash and Cash Equivalents
	Cash and cash equivalents are stated at cost. Cash equivalents consist of highly-liquid investments with an original maturity of three months or less when purchased.
	Allowance for Uncollectible Receivables
	The Company establishes an allowance for uncollectible receivables for the amounts of trade accounts receivable and other receivables that are not expected to be collected, based on past collection history, the economic environment and specified risks identified in the receivables portfolio. Receivables are considered past due if the full payment is not received by the contractual due date. At December 31, 2013 and 2012, the allowance for uncollectible receivables was insignificant.
	Inventories
	Coal and supplies inventories are valued at the lower of average cost or market. Coal inventory costs include labor, supplies, equipment costs, transportation costs incurred prior to the transfer of title to customers and operating overhead. The costs of removing overburden, called stripping costs, incurred during the production phase of the mine are considered variable production costs and are included in the cost of the coal extracted during the period the stripping costs are incurred.
	Investments and Membership Interests in Joint Ventures
	Investments and membership interests in joint ventures are accounted for under the equity method of accounting if the Company has the ability to exercise significant influence, but not control, over the entity. The Company's share of the entity's income or loss is reflected in "Other operating expense (income), net" in the consolidated statements of operations. Information about investment activity is provided in Note 9, " Equity Method Investments and Membership Interests in Joint Ventures"
	Investments in debt securities and marketable equity securities that do not qualify for equity method accounting are classified as available-for-sale and are recorded at their fair values. Unrealized gains and losses on these investments are recorded in other comprehensive income or loss. A decline in the value of an investment that is considered other-than-temporary would be recognized in operating expenses.
	Prepaid Royalties
	Leased mineral rights are often acquired through royalty payments. When royalty payments represent prepayments recoupable against future production, they are recorded as a prepaid asset, with amounts expected to be recouped within one year classified as current. When the coal is mined under these leases the royalties are recouped and the prepayment is charged to cost of sales.
	Acquired Sales Contracts
	Coal supply agreements (sales contracts) acquired in a business combination are capitalized at their fair value and amortized over the tons of coal shipped during the term of the contract. The fair value of a sales contract is determined by discounting the cash flows attributable to the difference between the contract price and the prevailing forward prices for the tons under contract at the date of acquisition. See Note 10, "Acquired Sales Contracts" for further information related to the Company's acquired sales contracts.
	Exploration Costs
	Costs to acquire permits for exploration activities are capitalized. Drilling and other costs related to locating coal deposits and evaluating the economic viability of such deposits are expensed as incurred.
	Property, Plant and Equipment
	Plant and Equipment
	Plant and equipment are recorded at cost. Interest costs incurred during the construction period for major asset additions are capitalized. We capitalized $15.9 million, $15.6 million, and $1.9 million of interest costs during the years ended December 31, 2013, 2012, and 2011, respectively. Expenditures that extend the useful lives of existing plant and equipment or increase the productivity of the asset are capitalized. The cost of maintenance and repairs that do not extend the useful life or increase the productivity of the asset are expensed as incurred.
	Preparation plants and loadouts are depreciated using the units-of-production method over the estimated recoverable reserves, subject to a minimum level of depreciation. Other plant and equipment are depreciated principally using the straight-line method over the estimated useful lives of the assets, limited by the remaining life of the mine. The useful lives of mining equipment, including longwalls, draglines and shovels, range from 5 to 32 years. The useful lives of buildings and leasehold improvements generally range from 10 to 30 years.
	Deferred Mine Development
	Costs of developing new mines or significantly expanding the capacity of existing mines are capitalized and amortized using the units-of-production method over the estimated recoverable reserves that are associated with the property being benefited. Costs may include construction permits and licenses; mine design; construction of access roads, shafts, slopes and main entries; and removing overburden to access reserves in a new pit. Additionally, deferred mine development includes the asset cost associated with asset retirement obligations.
	Coal Lands and Mineral Rights
	Rights to coal reserves may be acquired directly through governmental or private entities. A significant portion of the Company's coal reserves are controlled through leasing arrangements. Lease agreements are generally long-term in nature (original terms range from 10 to 50 years), and substantially all of the leases contain provisions that allow for automatic extension of the lease term providing certain requirements are met.
	The net book value of the Company's coal interests was $4.8 billion and $5.1 billion at December 31, 2013 and 2012. Payments to acquire royalty lease agreements and lease bonus payments are capitalized as a cost of the underlying mineral reserves and depleted over the life of proven and probable reserves. Coal lease rights are depleted using the units-of-production method, and the rights are assumed to have no residual value.
	Future lease bonus payments total $60.4 million in 2014, $75.8 million in 2015, $60.4 million in 2016, and $0.4 million in 2017.
	Depreciation, depletion and amortization.
	The depreciation, depletion and amortization related to long-lived assets is reflected in the statement of operations as a separate line item. No depreciation, depletion or amortization is included in any other operating cost categories.
	Impairment
	If facts and circumstances suggest that the carrying value of a long-lived asset or asset group may not be recoverable, the asset or asset group is reviewed for potential impairment. If this review indicates that the carrying amount of the asset will not be recoverable through projected undiscounted cash flows generated by the asset and its related asset group over its remaining life, then an impairment loss is recognized by reducing the carrying value of the asset to its fair value. The Company may, under certain circumstances, idle mining operations in response to market conditions or other factors. Because an idling is not a permanent closure, it is not considered an automatic indicator of impairment. See additional discussion in Note 5, "Impairment Charges and Mine Closure Costs".
	Goodwill
	In a business combination, goodwill represents the excess of the purchase price over the fair value assigned to the net tangible and identifiable intangible assets acquired. The Company tests goodwill for impairment annually as of the beginning of the fourth quarter, or when circumstances indicate a possible impairment may exist. If the results of the testing indicate that the carrying amount of a reporting unit exceeds the fair value of the reporting unit, the fair value of goodwill must be calculated. An impairment loss generally would be recognized when the carrying amount of goodwill exceeds the implied fair value of goodwill, determined by subtracting the fair value of the other assets and liabilities associated with the reporting unit from the total fair value of the reporting unit. The fair value of a reporting unit is determined using a discounted cash flow ("DCF") technique. A number of significant assumptions and estimates are involved in the application of the DCF analysis to forecast operating cash flows, including the discount rate, projections of production volumes, quality and costs to produce; projections of sales volumes by market (e.g., thermal versus metallurgical); and projections of market prices. See additional discussion in Note 6, "Goodwill."
	Deferred Financing Costs
	The Company capitalizes costs incurred in connection with new borrowings, the establishment or enhancement of credit facilities and the issuance of debt securities. These costs are amortized as an adjustment to interest expense over the life of the borrowing or term of the credit facility using the interest method. The unamortized balance of deferred financing costs was $99.2 million and $101.5 million at December 31, 2013 and 2012, respectively. Amounts classified as current were $19.7 million and $17.3 million at December 31, 2013 and 2012, respectively. Current amounts are recorded in "Other current assets" and noncurrent amounts are recorded in "Other noncurrent assets" in the accompanying consolidated balance sheets.
	Revenue Recognition
	Revenues include sales to customers of coal produced at Company operations and coal purchased from third parties. The Company recognizes revenue at the time risk of loss passes to the customer at contracted amounts. Transportation costs are included in cost of sales and amounts billed by the Company to its customers for transportation are included in revenues.
	Other Operating Expense (Income), Net
	Other operating expense (income), net in the accompanying consolidated statements of operations reflects income and expense from sources other than physical coal sales, including: bookouts, the practice of offsetting purchase and sale contracts for shipping convenience purposes, and contract settlements; royalties earned from properties leased to third parties; income from equity investments; gains and losses from dispositions of assets; and realized gains and losses on heating oil derivatives that do not qualify for hedge accounting and are not held for trading purposes.
	Asset Retirement Obligations
	The Company's legal obligations associated with the retirement of long-lived assets are recognized at fair value at the time the obligations are incurred. Accretion expense is recognized through the expected settlement date of the obligation. Obligations are incurred at the time development of a mine commences for underground and surface mines or construction begins for support facilities, refuse areas and slurry ponds. The obligation's fair value is determined using a DCF technique and is based upon permit requirements and various estimates and assumptions that would be used by market participants, including estimates of disturbed acreage, reclamation costs and assumptions regarding equipment productivity. Upon initial recognition of a liability, a corresponding amount is capitalized as part of the carrying value of the related long-lived asset.
	The Company reviews its asset retirement obligation at least annually and makes necessary adjustments for permit changes as granted by state authorities and for revisions of estimates of the amount and timing of costs. For ongoing operations, adjustments to the liability result in an adjustment to the corresponding asset. For idle operations, adjustments to the liability are recognized as income or expense in the period the adjustment is recorded. Any difference between the recorded obligation and the actual cost of reclamation is recorded in profit or loss in the period the obligation is settled. See additional discussion in Note 15, "Asset Retirement Obligations."
	Loss Contingencies
	The Company accrues for cost 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. The amount accrued represents the Company's best estimate of the loss, or, if no best estimate within a range of outcomes exists, the minimum amount in the range.
	Derivative Instruments
	The Company generally utilizes derivative instruments to manage exposures to commodity prices. Additionally, the Company may hold certain coal derivative instruments for trading purposes. Derivative financial instruments are recognized in the balance sheet at fair value. Certain coal contracts may meet the definition of a derivative instrument, but because they provide for the physical purchase or sale of coal in quantities expected to be used or sold by the Company over a reasonable period in the normal course of business, they are not recognized on the balance sheet.
	Certain derivative instruments are designated as the hedge instrument in a hedging relationship. In a fair value hedge, the Company hedges the risk of changes in the fair value of a firm commitment, typically a fixed-price coal sales contract. Changes in both the hedged firm commitment and the fair value of a derivative used as a hedge instrument in a fair value hedge are recorded in earnings. In a cash flow hedge, the Company hedges the risk of changes in future cash flows related to a forecasted purchase or sale. Changes in the fair value of the derivative instrument used as a hedge instrument in a cash flow hedge are recorded in other comprehensive income or loss. Amounts in other comprehensive income or loss are reclassified to earnings when the hedged transaction affects earnings and are classified in a manner consistent with the transaction being hedged. The Company formally documents the relationships between hedging instruments and the respective hedged items, as well as its risk management objectives for hedge transactions.
	The Company evaluates the effectiveness of its hedging relationships both at the hedge's inception and on an ongoing basis. Any ineffective portion of the change in fair value of a derivative instrument used as a hedge instrument in a fair value or cash flow hedge is recognized immediately in earnings. The ineffective portion is based on the extent to which exact offset is not achieved between the change in fair value of the hedge instrument and the cumulative change in expected future cash flows on the hedged transaction from inception of the hedge in a cash flow hedge or the change in the fair value. Ineffectiveness was insignificant for the years ended December 31, 2013, 2012 and 2011. See Note 11, "Derivatives" for further disclosures related to the Company's derivative instruments.
	Fair Value
	Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly hypothetical transaction between market participants at a given measurement date. Valuation techniques used must maximize the use of observable inputs and minimize the use of unobservable inputs. See Note 16, "Fair Values Measurements" for further disclosures related to the Company's recurring fair value estimates.
	Income Taxes
	Deferred income taxes are provided for temporary differences arising from differences between the financial statement amount and tax basis of assets and liabilities existing at each balance sheet date using enacted tax rates anticipated to be in effect when the related taxes are expected to be paid or recovered. A valuation allowance is established if it is more likely than not that a deferred tax asset will not be realized. In determining the need for a valuation allowance, the Company considers projected realization of tax benefits based on expected levels of future taxable income, available tax planning strategies and the reversal of temporary differences.
	Benefits from tax positions that are uncertain are not recognized unless the Company concludes that it is more likely than not that the position would be sustained in a dispute with taxing authorities, should the dispute be taken to the court of last resort. The Company would measure any such benefit at the largest amount of benefit that is greater than 50 percent likely of being realized upon settlement with taxing authorities.
	See Note 14, "Taxes" for further disclosures about income taxes.
	Benefit Plans
	The Company has non-contributory defined benefit pension plans covering most of its salaried and hourly employees. Benefits are generally based on the employee's age and compensation. The Company also currently provides certain postretirement medical and life insurance coverage for eligible employees. The cost of providing these benefits are determined on an actuarial basis and accrued over the employee's period of active service.
	The Company recognizes the overfunded or underfunded status of these plans as determined on an actuarial basis on the balance sheet and the changes in the funded status are recognized in other comprehensive income. See Note 20, "Employee Benefit Plans" for additional disclosures relating to these obligations.
	Stock-Based Compensation
	The compensation cost of all stock-based awards is determined based on the grant-date fair value of the award, and is recognized over the requisite service period. The grant-date fair value of option awards is determined using a Black-Scholes option pricing model. Compensation cost for an award with performance conditions is accrued if it is probable that the conditions will be met. See further discussion in Note 18, "Stock-Based Compensation and Other Incentive Plans."

Discontinued_Operations

Discontinued Operations	12 Months Ended
	Dec. 31, 2013
Discontinued Operations and Disposal Groups [Abstract]	'
Disposal Groups, Including Discontinued Operations, Disclosure [Text Block]	'
	Discontinued Operations
	As part of a strategy to divest its non-core thermal coal assets, the Company entered into a definitive agreement on June 27, 2013 to sell Canyon Fuel, to Bowie Resources, LLC. Canyon Fuel operated two longwall mining complexes and a continuous miner operation in Utah. The sale was completed on August 16, 2013, for $422.7 million in cash, including adjustments to working capital estimates.
	The following table summarizes the results of discontinued operations through the date of disposition:
			Year Ended December 31,
			2013		2012		2011
		(In thousands)
	Total Revenues		$	219,002	$	390,912	$	402,856
	Income from discontinued operations before income taxes		$	32,167	$	75,418	$	70,515
	Gain on sale		120,321		—		—
	Less: income tax expense		49,092		20,190		16,690
	Income from discontinued operations, including gain on sale - net of tax		$	103,396	$	55,228	$	53,825
	Basic earnings per common share from discontinued operations		$	0.49	$	0.26	$	0.28
	Diluted earnings per common share from discontinued operations		$	0.49	$	0.26	$	0.28
	The following table summarizes the assets and liabilities of the discontinued operations reflected in the December 31, 2012 consolidated balance sheet:
	Inventories	53,543
	Other current assets	10,763
	Net property, plant & equipment	280,109
	Other noncurrent assets	5,334
	Accounts payable and accrued expenses	27,419
	Other noncurrent liabilities	9,892
	The following table summarizes the results of discontinued operations through the date of disposition:
			Year Ended December 31,
			2013		2012		2011
		(In thousands)
	Total Revenues		$	219,002	$	390,912	$	402,856
	Income from discontinued operations before income taxes		$	32,167	$	75,418	$	70,515
	Gain on sale		120,321		—		—
	Less: income tax expense		49,092		20,190		16,690
	Income from discontinued operations, including gain on sale - net of tax		$	103,396	$	55,228	$	53,825
	Basic earnings per common share from discontinued operations		$	0.49	$	0.26	$	0.28
	Diluted earnings per common share from discontinued operations		$	0.49	$	0.26	$	0.28

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Abstract]	'
Comprehensive Income (Loss) Note [Text Block]	'
	Accumulated Other Comprehensive Income (Loss)
	Other comprehensive loss includes transactions recorded in stockholders' equity during the year, excluding net income and transactions with stockholders. In February 2013, the FASB issued ASU 2013-02, Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income. The standard requires that companies present, either parenthetically on the face of the financial statements or in a single note, the effect of significant amounts reclassified from each component of accumulated other comprehensive income and the income statement line items affected by the reclassification. The Company adopted the provisions of the new guidance in the first quarter of 2013.
	The following items are included in accumulated other comprehensive income (loss):
							Pension,
							Postretirement
							and Other						Accumulated
							Post-						Other
			Derivative				Employment			Available-			Comprehensive
			Instruments				Benefits			for-Sale Securities			Income (Loss)
			(In thousands)
	Balance at	1-Jan-11	$	(4,729	)		$	(4,676	)	$	1,455		$	(7,950	)
	Unrealized gains (losses)		4,320				(14,528		)	(1,924		)	(12,132		)
	Amounts reclassified from accumulated other comprehensive income (loss)		2,653				918			4			3,575
	Balance at	31-Dec-12	2,244				(18,286		)	(465		)	(16,507		)
	Unrealized gains		168				48,482			5,935			54,585
	Amounts reclassified from accumulated other comprehensive income (loss)		(1,847		)		916			545			(386		)
	Balance at	31-Dec-13	$	565			$	31,112		$	6,015		$	37,692
	The following amounts were reclassified out of accumulated other comprehensive income (loss) during the year ended December 31, 2013:
	Details about accumulated other			Reclassifications				Line Item in the Consolidated
	comprehensive income components			(in thousands)				Statement of Operations
	Derivative instruments			$	2,886			Revenues
				(1,039		)		Benefit from income taxes
				$	1,847			Net of tax
	Pension, postretirement and other post-employment benefits
	Amortization of prior service credits			$	13,705		1
	Amortization of actuarial gains (losses), net			(15,136		)	1
				(1,431		)		Total before tax
				515				Benefit from income taxes
				$	(916	)		Net of tax
	Available-for-sale securities			$	(852	)	2	Interest and investment income
				307				Benefit from income taxes
				$	(545	)		Net of tax
	1 Production-related benefits and workers' compensation costs are included in costs to produce coal. See Note 19, "Workers' Compensation Expense" and Note 20 "Employee Benefit Plans" for more information about pension, postretirement and postemployment benefit costs.
	2 The gains and losses on sales of available-for-sale-securities are determined on a specific identification basis.

Impairment_Charges_and_Mine_Cl

Impairment Charges and Mine Closure Costs	12 Months Ended
	Dec. 31, 2013
Impairment charges [Abstract]	'
Impairment Charges and Mine Closure Costs	'
	Impairment Charges and Mine Closure Costs
	Due to ongoing weakness in the thermal coal markets in Appalachia, the Company assessed in the third quarter of 2013 whether the carrying values of certain assets were recoverable through future cash flows. The Company determined that the carrying amounts of certain assets associated with the Hazard mining complex in Kentucky and the Company's ADDCAR subsidiary, which manufactures and sells its patented highwall mining system, could not be recovered through future cash flows expected to be generated from use of the assets and their ultimate disposal.
	The assets' fair values were determined based on projections of cash flows to be generated from use of the assets and their ultimate disposal including estimates relating to market demand, coal prices, production costs and mine plans, and recovery value of the assets. An impairment charge of $142.8 million was recognized to adjust the carrying value of the assets to their fair value of $71.3 million. These losses are reflected on the line "Asset impairment and mine closure costs" in the consolidated statements of operations.
	During 2013, the Company also recognized other-than-temporary impairment charges related to equity method investments. See further discussion in Note 9, "Equity Method Investments and Membership Interests in Joint Ventures."
	In 2012, the closure and idling of mines in Appalachia discussed in Note 1, "Basis of Presentation" resulted in closure costs and related impairment charges that are reflected on the line "Asset impairment and mine closures costs" in the consolidated statements of operations.
		In millions
	Parts and supplies inventory writedown	$	2.6
	Impairment of property, plant and equipment	95.6
	Impairment of coal properties and deferred development costs	403.3
	Royalty obligations	11.5
	Employee termination benefits	12.3
	Pension, postretirement and occupational disease curtailment gain, net	(1.8		)
		$	523.5
	In 2012, the value of an acquired sales contract was also determined to be impaired, see further discussion in Note 10, "Acquired Sales Contracts " for further discussion.
	The $7.3 million in asset impairment costs for the year ended December 31, 2011 related to a preparation plant and loadout of an acquired ICG mining operation that would not be used in ongoing operations.

Goodwill

Goodwill	12 Months Ended
	Dec. 31, 2013
Goodwill and Intangible Assets Disclosure [Abstract]	'
Goodwill	'
	Goodwill
	Changes in the carrying value of goodwill for the three years ended December 31, 2013 are as follows:
		(In thousands)
	Balance at January 1, 2011	$	114,963
	Consideration paid related to prior business acquisitions	829
	Acquisition of ICG	480,311
	Balance at December 31, 2011	596,103
	Impairment	(330,680		)
	Balance at December 31, 2012	265,423
	Impairment	(265,423		)
	Balance at December 31, 2013	$	—
	The Company performed its annual impairment testing as of October 1, 2013 on the two Appalachia reporting units with goodwill balances, the Leer mining complex and an undeveloped property adjacent to it. These two reporting units are sensitive to the volatility in the demand for and pricing of metallurgical coal. Continuing weakness in the metallurgical coal markets caused the Company to reassess key marketing and operating assumptions during the Company's annual budgeting process, which is the source of the projected cash flows for the goodwill impairment review. As a result, the book values of the reporting units exceeded their fair values after the first step of the goodwill impairment tests. It was also determined that the goodwill had no fair value, and the Company recognized an impairment loss for the remaining reporting units totaling $265.4 million.
	During the second quarter of 2012, a significant drop in the Company’s stock price, combined with continuing weak demand for thermal coal during the quarter and the Company’s resulting production cuts, indicated that the fair value of the Company’s goodwill could be less than its carrying value.  Accordingly, the Company performed the first step of the two-step goodwill impairment test as of June 30, 2012.  The value of the Company’s Black Thunder reporting unit in the Powder River Basin, where $115.8 million of goodwill had been allocated, was sensitive to market demand for thermal coal. The further weakening in thermal coal markets had significantly impacted the projected demand for and pricing of coal produced at Black Thunder.  In step one of the goodwill impairment testing, the fair value of the Black Thunder reporting unit did not exceed its carrying value, primarily due to the impact of lower demand on near term sales volumes and pricing.  The Company recorded an impairment charge for the entire $115.8 million carrying value of Black Thunder's goodwill in 2012.
	During 2012, metallurgical prices fell substantially from the peaks reached during 2011, when the reporting units were acquired with the Company's purchase of ICG. Because the goodwill amounts allocated to certain reporting units in the Company’s Appalachia segment acquired with the ICG acquisition were sensitive to volatility in the demand for metallurgical coal, the fair values of two of these reporting units fell below their carrying value. The allocated goodwill of $214.9 million for those reporting units was determined to be fully impaired, based on the discounted cash flows used in the ICG acquisition valuation, adjusted for current market conditions and estimates of production levels.

Inventories

Inventories	12 Months Ended
	Dec. 31, 2013
Inventory Disclosure [Abstract]	'
Inventories	'
	Inventories
	Inventories consist of the following:
		31-Dec
		2013		2012
		(In thousands)
	Coal	$	117,531	$	180,917
	Repair parts and supplies	137,497		172,139
	Work-in-process	9,133		12,368
		$	264,161	$	365,424
	The repair parts and supplies are stated net of an allowance for slow-moving and obsolete inventories of $8.4 million at December 31, 2013 and $12.6 million at December 31, 2012.

Investments_in_AvailableforSal

Investments in Available-for-Sale Securities	12 Months Ended
	Dec. 31, 2013
Available-for-sale Securities [Abstract]	'
Available-for-sale Securities [Text Block]	'
	Investments in Available-for-Sale Securities
	The Company has invested in marketable debt securities, primarily highly liquid AA - rated corporate bonds and U.S. government and government agency securities. These investments are held in the custody of a major financial institution. These securities, along with the Company's investments in marketable equity 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:
		December 31, 2013
											Balance Sheet
				Gross		Gross					Classification
				Unrealized		Unrealized			Fair		Short-Term		Other
		Cost Basis		Gains		Losses			Value		Investments		Assets
		(In thousands)
	Available-for-sale:
	U.S. government and agency securities	$	65,002	$	12	$	(75	)	$	64,938	$	64,938	$	—
	Corporate notes and bonds	184,773		6		(1,304		)	183,476		183,476		—
	Equity securities	5,271		13,660		(2,902		)	16,029		—		16,029
	Total Investments	$	255,046	$	13,678	$	(4,281	)	$	264,443	$	248,414	$	16,029
		December 31, 2012
											Balance Sheet
				Gross		Gross					Classification
				Unrealized		Unrealized			Fair		Short-Term		Other
		Cost Basis		Gains		Losses			Value		Investments		Assets
		(In thousands)
	Available-for-sale:
	U.S. government and agency securities	$	146,993	$	2	$	(412	)	$	146,583	$	146,583	$	—
	Corporate notes and bonds	88,118		—		(396		)	87,722		87,722		—
	Equity securities	5,271		2,704		(2,628		)	5,347		—		5,347
	Total Investments	$	240,382	$	2,706	$	(3,436	)	$	239,652	$	234,305	$	5,347
	The aggregate fair value of investments with unrealized losses that have been owned for less than a year was $164.3 million and $223.3 million at December 31, 2013 and December 31, 2012, respectively. The aggregate fair value of investments with unrealized losses that have been owned for over a year was $48.7 million and $0.4 million at December 31, 2013 and December 31, 2012, respectively.
	The debt securities outstanding at December 31, 2013 have maturity dates ranging from the first quarter of 2014
	through the first quarter of 2015. 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.

Equity_Investments_and_Members

Equity Investments and Membership Interests in Joint Ventures	12 Months Ended
	Dec. 31, 2013
Equity Method Investments and Joint Ventures [Abstract]	'
Equity Investments and Membership Interests in Joint Ventures	'
	Equity Method Investments and Membership Interests in Joint Ventures
	The Company accounts for its investments and membership interests in joint ventures under the equity method of accounting if the Company has the ability to exercise significant influence, but not control, over the entity. Equity method investments are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the investments may not be recoverable. Certain of the Company's investments are in development stage companies whose success depends on factors including receipt of permits and other regulatory environment issues, the ability of the investee companies to raise additional funds in financial markets that can be volatile, and other key business factors.
	Below are the equity method investments reflected in the consolidated balance sheets:
	Investee		Knight Hawk				DKRW				DTA			Tenaska			Millennium			Tongue River			Other		Total
	Balance at December 31, 2010		$	131,250			$	21,961			$	14,472		$	9,768		$	—		$	—		$	—	$	177,451
	Investments in affiliates		—				—				—			5,500			25,000			12,989			—		43,489
	Advances to (distributions from) affiliates, net		(16,621		)		—				6,498			—			3,477			—			—		(6,646		)
	Equity in comprehensive income (loss)		20,596				(2,246		)		(4,884		)	(2		)	(2,153		)	—			—		11,311
	Balance at December 31, 2011		135,225				19,715				16,086			15,266			26,324			12,989			—		225,605
	Investments in affiliates		—				—				—			—			—			—			—		—
	Advances to (distributions from) affiliates, net		(7,151		)		—				4,335			—			8,798			1,708			—		7,690
	Equity in comprehensive income (loss)		20,989				(4,200		)		(4,959		)	(2		)	(2,908		)	—			—		8,920
	Balance at December 31, 2012		149,063				15,515				15,462			15,264			32,214			14,697			—		242,215
	Advances to (distributions from) affiliates, net		(13,536		)		—				3,644			—			6,476			4,004			200		788
	Equity in comprehensive income (loss)		17,279				(1,832		)		(4,969		)	—			(2,796		)	(282		)	—		7,400
	Impairment of equity investment		—				(13,683		)		—			(15,264		)	—			—			—		(28,947		)
	Balance at December 31, 2013		$	152,806			$	—			$	14,137		$	—		$	35,894		$	18,419		$	200	$	221,456
	The Company holds a 49% equity interest in Knight Hawk Holdings, LLC ("Knight Hawk"), a coal producer in the Illinois Basin.
	The Company holds a 24% equity interest in DKRW Advanced Fuels LLC ("DKRW"), a company engaged in developing coal-to-liquids facilities. DKRW has borrowed funds from the Company under a convertible secured promissory note. Amounts borrowed are due and payable in cash or in additional equity interests upon the closing of DKRW's next financing, bear interest at the rate of 15% per annum, and are secured by DKRW's equity interests in Medicine Bow Fuel & Power LLC. The note balance was $38.7 million at December 31, 2012. DKRW Advanced Fuels, LLC ("DKRW") had previously entered into an Engineering, Procurement and Construction Agreement with a Chinese company to construct and commission the Medicine Bow coal-to-liquids facility. However, as the project did not progress to the next stage of development, the Company recorded an other-than-temporary impairment charge of $57.7 million in the third quarter of 2013, which includes the Company's 24% equity investment of $13.7 million and the outstanding $44.0 million loan receivable balance. The impairment charges are included on the line "Asset impairment and mine closure costs" in the consolidated statement of operations.
	The Company holds a general partnership interest of 21.875% in Dominion Terminal Associates ("DTA"), which is accounted for under the equity method. DTA operates a ground storage-to-vessel coal transloading facility in Newport News, Virginia for use by the partners. Under the terms of a throughput and handling agreement with DTA, each partner is charged its share of cash operating and debt-service costs in exchange for the right to use the facility's loading capacity and is required to make periodic cash advances to DTA to fund such costs.
	The Company holds a 35% ownership interest in Tenaska Trailblazer Partners, LLC ("Tenaska"), the developer of the Trailblazer Energy Center, a proposed fossil-fuel-based electric power plant near Sweetwater, Texas. During the second quarter of 2013, Tenaska announced that it was discontinuing its development plans for the Trailblazer Energy Center in Texas. As a result, the Company recorded a $20.5 million impairment charge, which consisted of its 35% equity investment of $15.3 million and a $5.2 million receivable balance related to advances for development work. The impairment charges are included on the line "Asset impairment and mine closure costs" in the consolidated statement of operations.
	In January 2011, the Company purchased a 38% ownership interest in Millennium Bulk Terminals-Longview, LLC ("Millennium"), the owner of a brownfield bulk commodity terminal on the Columbia River near Longview, Washington, for $25.0 million, plus additional future consideration upon the completion of certain project milestones. Millennium continues to work on obtaining the required approvals and necessary permits to complete dredging and other upgrades to enable coal, alumina and cementitious material shipments through the terminal. The Company will control 38% of the terminal's throughput and storage capacity, in order to facilitate export shipments of coal off the west coast of the United States.
	In July 2011, the Company purchased a 35% membership interest in the Tongue River Holding Company, LLC ("Tongue River") joint venture. Tongue River will develop and construct a railway line near Miles City, Montana and the Company's Otter Creek reserves. The Company has the right, upon the receipt of permits and approval for construction or under other prescribed circumstances, to require the other investors to purchase all of the Company's units in the venture at an amount equal to the capital contributions made by the Company at that time, less any distributions received.
	Summarized financial information of the Company's equity method investees follows:
		31-Dec
		2013				2012				2011
		(In thousands)
	Condensed combined income statement information:
	Revenues	$	208,289			$	190,661			$	184,358
	Gross profit	10,234				15,308				19,495
	Income from operations	6,574				8,898				13,180
	Net income	(397		)		641				6,788
	Condensed combined balance sheet information:
	Current assets	$	52,413			$	78,961
	Noncurrent assets	398,495				387,884
	Total assets	$	450,908			$	466,845
	Current liabilities	$	31,243			$	57,403
	Noncurrent liabilities	131,445				128,489
	Equity	287,903				280,690
	Noncontrolling interest	317				263
	Total liabilities and equity	$	450,908			$	466,845
	The Company may be required to make future contingent payments of up to $58.5 million related to development financing for certain of its equity investees. The Company’s obligation to make these payments, as well as the timing of any payments required, is contingent upon the achievement of project development milestones, which can be affected by the factors named above.

Acquired_Sales_Contracts

Acquired Sales Contracts	12 Months Ended
	Dec. 31, 2013
Acquired Sales Contracts [Abstract]	'
aci_DescriptionAcquiredSalesContractsTextBlock [Text Block]	'
	Acquired Sales Contracts
	The acquired sales contracts reflected in the consolidated balance sheets are as follows:
		December 31, 2013						December 31, 2012
		Assets			Liabilities			Assets			Liabilities
		(In thousands)						(In thousands)
	Acquired fair value	$	131,819		$	166,697		$	131,819		$	166,697
	Accumulated amortization	(129,449		)	(120,367		)	(123,776		)	(105,237		)
	Total	$	2,370		$	46,330		$	8,043		$	61,460
	Net total				$	(43,960	)				$	(53,417	)
	Balance Sheet classification:
	Other current	$	1,324		$	14,373		$	5,651		$	14,038
	Other noncurrent	$	1,046		$	31,957		$	2,392		$	47,422
	In 2012, the Company recognized an impairment loss of $15.7 million to write off a contract acquired with the ICG acquisition with an original acquired fair value of $17.5 million.
	The Company anticipates amortization of acquired sales contracts, based upon expected shipments in the next five years, to be income of approximately $21.5 million in 2014, $6.7 million in 2015, $2.8 million in 2016, and $3.3 million in 2017 and $3.1 million in 2018.

Derivatives

Derivatives	12 Months Ended
	Dec. 31, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Derivatives	'
	Derivatives
	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 57 to 67 million gallons of diesel fuel for use in its operations during 2014. 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 December 31, 2013, the Company had protected the price of approximately 91% of its expected purchases for 2014 and 10% of its expected 2015 purchases. At December 31, 2013, the Company had purchased heating oil call options for approximately 63 million gallons for the purpose of managing the price risk associated with future diesel purchases.
	The Company has also purchased heating oil call options to manage the price risk associated with fuel surcharges on its barge and rail shipments, which cover increases in diesel fuel prices for the respective carriers. At December 31, 2013, the Company held heating oil call options for 5.1 million gallons that will settle ratably in 2014 for the purpose of managing the fluctuations in cash flows associated with fuel surcharges on future shipments.
	These positions reduce the Company’s risk of cash flow fluctuations related to these surcharges but the positions are not accounted for as hedges.
	Coal 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 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 December 31, 2013, the Company held derivatives for risk management purposes that are expected to settle in the following years:
	(Tons in thousands)		2014			2015			Total
	Coal sales		4,845			900			5,745
	Coal purchases		1,561			—			1,561
	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 unrecognized gains of $9.6 million in the trading portfolio are expected to be realized in 2014.
	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 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 consolidated balance sheets. The fair value and location of derivatives reflected in the accompanying consolidated balance sheets are as follows:
			31-Dec-13											31-Dec-12
	Fair Value of Derivatives		Asset				Liability							Asset				Liability
	(In thousands)		Derivative				Derivative							Derivative				Derivative
	Derivatives Designated as Hedging Instruments
	Coal		$	909			$	(26	)					$	3,277			$	(10	)
	Derivatives Not Designated as Hedging Instruments
	Heating oil -- diesel purchases		4,681				—							7,379				—
	Heating oil -- fuel surcharges		422				—							1,961				—
	Coal -- held for trading purposes		55,327				(45,763		)					17,403				(16,933		)
	Coal -- risk management		6,342				(1,950		)					24,843				(7,342		)
	Total		66,772				(47,713		)					51,586				(24,275		)
	Total derivatives		67,681				(47,739		)					54,863				(24,285		)
	Effect of counterparty netting		(47,727		)		47,727							(22,548		)		22,548
	Net derivatives as classified in the balance sheets		$	19,954			$	(12	)		$	19,942		$	32,315			$	(1,737	)		$	30,578
					31-Dec-13				31-Dec-12
	Net derivatives as reflected on the balance sheets
	Heating oil		Other current assets		$	5,103			$	9,340
	Coal		Coal derivative assets		14,851				22,975
			Coal derivative liabilities		(12		)		(1,737		)
					$	19,942			$	30,578
	The Company had a current asset for the right to reclaim cash collateral of $2.2 million and $16.2 million at December 31, 2013 and 2012, respectively. These amounts are not included with the derivatives presented in the table above and are included in “other current assets” in the accompanying consolidated balance sheets.
	The effects of derivatives on measures of financial performance are as follows:
	Derivatives used in Cash Flow Hedging Relationships (in thousands)
	For the year ended December 31
			Gain (Loss) Recognized in Other Comprehensive Income(Effective Portion)													Gains (Losses) Reclassified from Other Comprehensive Income into Income
																(Effective Portion)
			2013				2012				2011					2013				2012				2011
	Coal sales	(1)	$	(338	)		$	7,690			4,923					$	3,664			$	2,675			$	1,572
	Coal purchases	(2)	526				(2,440		)		(2,009		)			(683		)		—				—
			$	188			$	5,250			$	2,914				$	2,981			$	2,675			$	1,572
	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 year ended December 31, 2013 and 2012.
	Derivatives Not Designated as Hedging Instruments (in thousands)
	For the year ended December 31
			Gain (Loss) Recognized
			2013				2012				2011
	Coal — unrealized	(3)	$	(12,700	)		$	8,272			$	6,438
	Coal — realized	(4)	$	32,534			$	43,990			$	(7	)
	Heating oil — diesel purchases	(4)	$	(9,791	)		$	(22,281	)		$	(2,906	)
	Heating oil — fuel surcharges	(4)	$	(947	)		$	(2,209	)		$	—
	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, net
	During the first quarter of 2012, the Company determined that the effectiveness of heating oil options as a hedge for diesel fuel purchases could not be established as of December 31, 2011. As a result, the amount remaining in accumulated other comprehensive income of $8.2 million was recorded in the "Other operating income, net" line in the consolidated statement of operations, or $5.2 million, net of income taxes. In 2011, unrealized gains of $1.3 million were recognized in other comprehensive income and gains of $14.9 million were reclassified from other comprehensive income into earnings relating to heating oil positions.
	The Company recognized net unrealized and realized gains of $4.9 million and $8.3 million during the year ended December 31, 2013 and 2012, respectively, related to its trading portfolio, which are included in the caption “Change in fair value of coal derivatives and coal trading activities, net” in the accompanying consolidated statements of operations, and are not included in the previous tables reflecting the effects of derivatives on measures of financial performance.
	Based on fair values at December 31, 2013, gains on derivative contracts designated as hedge instruments in cash flow hedges of approximately $0.8 million are expected to be reclassified from other comprehensive income into earnings during the next twelve months.

Accrued_Expenses_and_Other_Cur

Accrued Expenses and Other Current Liabilities	12 Months Ended
	Dec. 31, 2013
Accrued Expenses and Other Current Liabilities [Abstract]	'
Accounts Payable and Accrued Liabilities Disclosure [Text Block]	'
	Accrued Expenses and Other Current Liabilities
	Accrued expenses and other current liabilities consist of the following:
		December 31,
		2013		2012
		(In thousands)
	Payroll and employee benefits	$	67,621	$	72,405
	Taxes other than income taxes	114,664		121,029
	Interest	18,528		42,413
	Acquired sales contracts	14,373		14,038
	Workers’ compensation	12,434		10,371
	Asset retirement obligations	24,940		38,920
	Other	26,015		18,842
		$	278,575	$	318,018

Debt_and_Financing_Arrangement

Debt and Financing Arrangements	12 Months Ended
	Dec. 31, 2013
Debt Disclosure [Abstract]	'
Debt	'
	Debt and Financing Arrangements
		December 31,
		2013		2012
		(In thousands)
	Term loan due 2018 ($1.93 billion and $1.65 billion face value, respectively)	$	1,906,975	$	1,627,384
	8.75% senior notes ($600.0 million face value) due 2016	—		590,999
	7.00% senior notes due 2019 at par	1,000,000		1,000,000
	8.00% senior secured notes due 2019 at par	350,000		—
	9.875% senior notes ($375.0 million face value) due 2019	362,358		360,042
	7.25% senior notes due 2020 at par	500,000		500,000
	7.25% senior notes due 2021 at par	1,000,000		1,000,000
	Other	32,162		40,350
		5,151,495		5,118,775
	Less current maturities of debt	33,493		32,896
	Long-term debt	$	5,118,002	$	5,085,879
	On December 17, 2013, the Company entered into an amendment of the credit agreement governing its term loan and revolving credit facility whereby the term loan facility was increased to accommodate an incremental $300.0 million aggregate principal loan at 98% of the face amount and commitments under the revolving credit facility were reduced to $250.0 million from $350.0 million. Also on December 17, 2013, the Company issued $350.0 million aggregate principal amount of 8.00% senior secured second lien notes due 2019 (the “2019 Secured Notes”) at par.  Interest on the 2019 Secured Notes is payable on January 15 and July 15 of each year, beginning on July 15, 2014. The 2019 Secured Notes are secured by the same assets that secure indebtedness under the senior secured credit facility, but on a second priority basis, subject to certain exceptions and permitted liens.With the proceeds from these transactions, the Company retired the outstanding $600 million in aggregate principal amount of 8.75% senior unsecured notes due 2016 (“2016 Notes”) for $628.7 million.
	Credit Facilities
	Borrowings under the Company's senior secured revolving credit facility bear interest at a floating rate based on LIBOR determined by reference to the Company's leverage ratio, as calculated in accordance with the underlying amended credit agreement. The credit facility's term expires on June 14, 2016 and is secured by substantially all of the Company's assets as well as its ownership interests in substantially all of its subsidiaries. Commitment fees of 0.50% to 0.75% per annum are payable on the average unused daily balance of the revolving credit facility.
	The Company maintains an accounts receivable securitization program under which eligible trade receivables are sold, without recourse, to a multi‑seller, asset‑backed commercial paper conduit. The entity through which these receivables are sold is consolidated into the Company's financial statements. The Company may borrow and draw letters of credit against the facility, and pays facility fees, program fees and letter of credit fees (based on amounts of outstanding letters of credit). The total aggregate borrowings and letters of credit are limited by eligible accounts receivable, as defined under the terms of the agreement. The credit facility supporting the borrowings under the program is subject to renewal annually, and expires on December 9, 2014.
	Financial covenant requirements may restrict the amount of unused capacity available to the Company for borrowings and letters of credit. The amendments on December 17, 2013 relaxed financial maintenance covenants, with only a minimum liquidity test and beginning June, 2015, a maximum secured leverage ratio test. The amendment also limits dividends to one cent per share per fiscal year.
	At December 31, 2013, the available borrowing capacity under the Company's lines of credit was approximately $253.4 million.
	Term Loan
	On May 16, 2012, the Company borrowed $1.4 billion under a secured term loan facility, issued at a 1% discount. The proceeds from the term loan were used to retire all outstanding borrowings under the revolving credit facility and the outstanding $450.0 million principal amount of 6.75% Senior Notes due 2013 issued by Arch Western Finance, LLC (“Arch Western Finance”), the Company’s indirect subsidiary. On November 21, 2012, the Company borrowed an incremental $250.0 million on the term loan facility at a 1% discount at the same rate as the initial borrowing.
	The term loan contains no financial maintenance covenants, is prepayable and is secured by the same assets as borrowings under the revolving credit facility.  Quarterly principal payments of $3.5 million began in September 2012, increased to $4.125 million per quarter as a result of the incremental borrowing in November, 2012, and increased further to $4.875 million with the December 17, 2013 borrowing.  A balloon payment of $1.85 billion is due in May, 2018. Interest is payable at a rate of the greater of a LIBOR-based rate or 1.25%, plus 500 basis points.
	2019 9.875% Notes
	On November 21, 2012, the Company issued $375.0 million aggregate principal amount of 9.875% senior unsecured notes due 2019 (the “2019 9.875% Notes”) at an issue price of 95.934% of the face amount. Interest is payable on the 2019 9.875% Notes annually on June 15 and December 15. At any time on or after December 15, 2016, the Company may redeem some or all of the notes. The redemption price, reflected as a percentage of the principal amount, is: 104.938%for notes redeemed between December 15, 2016 and December 14, 2017; 102.469% for notes redeemed between December 15, 2017 and December 14, 2018; and 100% for notes redeemed on or after December 15, 2018. In addition, at any time and on one or more occasions prior to December 15, 2015, the Company may redeem an aggregate principal amount of senior notes not to exceed 35% of the original aggregate principal amount of the senior notes outstanding with the proceeds of one or more public equity offerings, at a redemption price equal to 109.875%.
	The unsecured senior notes are guaranteed by substantially all of the Company's subsidiaries, except for Arch Receivable Company, LLC, which is the conduit for the accounts receivable securitization program, and the Company's subsidiaries outside the U.S.
	2019 Secured Notes
	Interest is payable on the 2019 Secured Notes on January 15 and July 15 of each year, commencing July 15, 2014. The Company may redeem some or all of the notes during the noted 12 month periods at prices that are reflected as a percentage of the principal amount, as follows: 104.0% commencing January 15, 2016, 102.0% commencing January 15, 2017, and 100% thereafter.
	2020 Notes
	The Company has outstanding $500.0 million in aggregate principal amount of 7.25% senior unsecured notes due in 2020 (“2020 Notes”) at par. Interest is payable on the 2020 Notes on April 1 and October 1 of each year. The Company may redeem some or all of the notes during the respective 12 month periods at prices that are reflected as a percentage of the principal amount, as follows: 103.625% commencing October 1, 2015; 102.417% commencing October 1, 2016; 101.208% commencing October 1, 2017; and 100% thereafter.
	2019 7% and 2021 Notes
	On June 14, 2011, the Company issued $1.0 billion of 7.00% unsecured senior notes due 2019 (“2019 7% Notes”) and $1.0 billion of 7.25% unsecured senior notes due 2021 (“2021 Notes”) at their face amount. These notes were used to finance, along with an issuance of common stock discussed in Note 15, "Capital Stock", the acquisition of ICG. Interest is payable on the 2019 7% Notes and 2021 Notes on June 15 and December 15 of each year.
	At any time prior to June 15, 2014, the Company may redeem up to 35% of the original aggregate principal amount of each of the 2019 7% Notes and 2021 Notes, plus accrued and unpaid interest, with the net proceeds from certain equity offerings, at a redemption price, reflected as a percentage of the principal amount, equal to 107.0% and 107.25%, respectively. The Company may redeem the 2019 7% Notes prior to June 15, 2015 and the 2021 Notes prior to June 15, 2016 at the respective make-whole prices set forth in the indenture. The Company may redeem some or all of the 2019 7% Notes during the noted 12 month periods at prices that are reflected as a percentage of the principal amount, as follows: 103.5% commencing June 15, 2015; 101.75% commencing June 15, 2016; and 100% thereafter. The Company may redeem some or all of the 2021 Notes during the noted 12 month periods at prices that are reflected as a percentage of the principal amount, as follows: 103.625% commencing June 15, 2016; 102.417% commencing June 15, 2017; 101.208% commencing June 15, 2018 and 100% after June 15, 2019. In each case, accrued and unpaid interest at the redemption date is due upon redemption.
	Other Debt Retirements
	On May 16, 2012, Arch Western Finance accepted for purchase an aggregate of approximately $304.0 million principal amount of its 6.75% Senior Notes due 2013 in an initial settlement pursuant to the terms of its tender offer and consent solicitation, which commenced on May 1, 2012; and called for the redemption of the remaining outstanding 6.75% Senior Notes due 2013 after the completion of the tender offer.  The consideration for each $1,000 of principal purchased under the tender offer and consent solicitation was $1,002.50, for a total purchase consideration of $308.0 million.  On May 30, 2012, the remaining notes with an outstanding principal amount of $146.0 million were redeemed at par value.
	Upon ICG's acquisition, the Company gave a 30-day redemption notice to the Trustee of ICG's 9.125% senior notes and legally discharged its obligation under the 9.125% senior notes by depositing the required funds with the Trustee to redeem the debt. On July 14, 2011, all of the outstanding 9.125% senior notes were redeemed at an aggregate price of $251.4 million, including the required make-whole premium, plus accrued interest of $5.2 million.
	At its acquisition date, ICG's 4.00% convertible senior notes with a fair value of $298.5 million and 9.00% convertible senior notes with a fair value of $1.7 million (“convertible notes”) became convertible into cash, pursuant to the amended indentures governing the convertible notes, at a calculated conversion rate of $2,614.6848 for each $1,000 in principal amount surrendered for conversion for the 4.00% convertible notes and $2,392.734 for the 9.00% convertible notes for conversions occurring prior to August 17, 2011.
	At the acquisition date, other ICG debt had a fair value of approximately $54.0 million and consisted mainly of equipment notes and insurance notes payable.
	Any remaining amounts outstanding under the convertible notes and other ICG debt is included in “other” in the debt table above.
	Debt Maturities
	Expected aggregate maturities of debt for the next five years are $33.5 million in 2014, $24.0 million in 2015, $24.0 million in 2016, $23.7 million in 2017 and $1.9 billion in 2018.
	Debt Covenants
	Terms of the Company's credit facilities and leases contain financial and other covenants that limit the ability of the Company to, among other things, acquire, dispose, merge or consolidate assets; incur additional debt; pay dividends and make distributions or repurchase stock; make investments; create liens; issue and sell capital stock of subsidiaries; enter into restrictions affecting the ability of restricted subsidiaries to make distributions, loans or advances to the Company; engage in transactions with affiliates and enter into sale and leaseback transactions. In addition, the covenants require the Company to pledge assets to collateralize the revolving credit and term loan facilities. The assets pledged include equity interests in wholly‑owned subsidiaries, certain real property interests, accounts receivable and inventory of the Company. Failure by the Company to comply with such covenants could result in an event of default, which, if not cured or waived, could have a material adverse effect on the Company.
	Financing Costs
	The Company paid financing costs of $20.5 million, $50.6 million and $114.8 million in conjunction with its financing activities during the year ended December 31, 2013, 2012 and 2011, respectively. The Company's financing fees are generally deferred, however, the Company incurred a fee of $49.5 million in 2011 in conjunction with the acquisition of ICG that was expensed, as the related bridge financing facility was not used.
	During the year ended December 31, 2013 and 2012, the Company wrote off deferred financing costs of $5.4 million and $1.1 million, respectively, and $6.9 million of unamortized discount and $0.8 million of unamortized issue premium, respectively, related to the redemption of senior notes. In addition, the Company wrote off $1.9 million and $23.4 million of deferred financing costs relating to the reduction in capacity of the senior secured revolving credit facility during the year ended December 31, 2013 and 2012 respectively. The Company recognized a net loss of $2.0 million during the year ended December 31, 2011 on the early extinguishment of ICG's debt, including the conversions of the 4.00% and 9.00% convertible notes. The write-off of deferred financing fees, along with other transaction fees associated with these transactions, is reflected in line “Net loss resulting from early retirement and refinancing of debt” in the consolidated statements of operations.

Taxes

Taxes	12 Months Ended
	Dec. 31, 2013
Taxes [Abstract]	'
Income Tax Disclosure [Text Block]	'
	Taxes
	The Company is subject to U.S. federal income tax as well as income tax in multiple state jurisdictions. The tax years 2002 through 2013 remain open to examination for U.S. federal income tax matters and 1998 through 2013 remain open to examination for various state income tax matters.
	Significant components of the provision for (benefit from) income taxes are as follows:
		Year Ended December 31
		2013			2012			2011
		(In thousands)
	Current:
	Federal	$	—		$	(20,022	)	$	(24,449	)
	State	(647		)	575			1,072
	Total current	(647		)	(19,447		)	(23,377		)
	Deferred:
	Federal	(318,956		)	(341,486		)	1,544
	State	(15,895		)	7,026			(2,446		)
	Total deferred	(334,851		)	(334,460		)	(902		)
		$	(335,498	)	$	(353,907	)	$	(24,279	)
	A reconciliation of the statutory federal income tax provision (benefit) at the statutory rate to the actual provision for (benefit from) income taxes follows:
		Year Ended December 31
		2013			2012			2011
		(In thousands)
	Income tax provision (benefit) at statutory rate	$	(378,463	)	$	(382,581	)	$	22,253
	Percentage depletion allowance	(15,796		)	(33,654		)	(53,156		)
	Goodwill	70,301			56,916			—
	State taxes, net of effect of federal taxes	(25,265		)	(24,231		)	(3,790		)
	Change in valuation allowance	8,659			31,832			2,416
	Other, net	5,066			(2,189		)	7,998
		$	(335,498	)	$	(353,907	)	$	(24,279	)
	In 2013, 2012 and 2011, compensatory stock options and other equity based compensation awards were exercised resulting in a tax expense (benefit) of $1.5 million, $0.3 million and $(0.4) million, respectively. The tax benefit will be recorded in paid-in capital at such point in time when a cash tax benefit is recognized.
	Significant components of the Company's deferred tax assets and liabilities that result from carryforwards and temporary differences between the financial statement basis and tax basis of assets and liabilities are summarized as follows:
		December 31,
		2013			2012
		(In thousands)
	Deferred tax assets:
	Net operating loss carryforwards	$	660,916		$	496,330
	Alternative minimum tax credit carryforwards	126,755			150,014
	Reclamation and mine closure	113,843			104,570
	Goodwill	52,636			43,839
	Acquired sales contracts	33,392			38,735
	Workers' compensation	31,641			32,241
	Retiree benefit plans	20,527			32,087
	Share based compensation	28,494			25,440
	Contract obligations	19,327			21,798
	Other, primarily accrued liabilities	68,969			66,777
	Gross deferred tax assets	1,156,500			1,011,831
	Valuation allowance	(43,322		)	(34,663		)
	Total deferred tax assets	1,113,178			977,168
	Deferred tax liabilities:
	Plant and equipment	1,364,382			1,411,446
	Deferred development	91,126			77,013
	Investment in tax partnerships	8,170			72,513
	Other	13,902			13,018
	Total deferred tax liabilities	1,477,580			1,573,990
	Net deferred liability	$	364,402		$	596,822
	Current asset	$	49,144		$	67,360
	Non-current deferred tax liability	$	413,546		$	664,182
	The Company has federal net operating loss carryforwards for regular income tax purposes of $1.8 billion at December 31, 2013 that will expire between 2022 and 2033. The Company has an alternative minimum tax credit carryforward of $126.7 million at December 31, 2013, which has no expiration date and can be used to offset future regular tax in excess of the alternative minimum tax.
	The Company has recorded a valuation allowance for a portion of its deferred tax assets that management believes, more likely than not, will not be realized. Management reassesses the ability to realize its deferred tax assets annually in the fourth quarter or when circumstances indicate that the ability to realize deferred tax assets has changed. This review resulted in increases (decreases) in the valuation allowance of $8.7 million, $31.8 million and $2.1 million in 2013, 2012 and 2011, respectively. The valuation allowance relates to certain state and foreign net operating loss benefits.
	A reconciliation of the beginning and ending amounts of gross unrecognized tax benefits follows:
		(In thousands)
	Balance at January 1, 2011	$	4,418
	Additions based on tax positions related to the current year	1,626
	Additions for tax positions of prior years	2,754
	Balance at December 31, 2011	8,798
	Additions based on tax positions related to the current year	409
Additions for tax positions of prior years	21,943
Balance at December 31, 2012	31,150
Additions based on tax positions related to the current year	1,199
Additions for tax positions of prior years	688
Reductions as a result of lapses in the statute of limitations	(1,248		)
Balance at December 31, 2013	$	31,789
If recognized, the entire amount of the gross unrecognized tax benefits at December 31, 2013 would affect the effective tax rate.
The Company recognizes interest and penalties related to unrecognized tax benefits in income tax expense. The Company had accrued interest and penalties of $1.3 million and $1.0 million at December 31, 2013 and 2012, respectively, of which $0.3 million, $0.2 million and $0.2 million was recognized as expense during 2013, 2012, and 2011. In the next 12 months, no gross unrecognized tax benefits are expected to be reduced due to the expiration of the statute of limitations.
During 2008, the Company reached a settlement with the IRS regarding the Company's treatment of acquired coal operations and their simultaneous combination with the Company's Wyoming operations into the Arch Western joint venture. The settlement involved a re-characterization of deferred tax assets, including an increase in net operating loss carryforwards of $145.1 million and other amortizable assets that provided additional tax deductions through 2013. A portion of these cash tax benefits accrued to ARCO pursuant to the original purchase agreement, including $0.8 million paid in 2011 that was recorded as an addition to goodwill.

Asset_Retirement_Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2013
Asset Retirement Obligation [Abstract]	'
Asset Retirement Obligation Disclosure [Text Block]	'
	Asset Retirement Obligations
	The Company's asset retirement obligations arise from the Federal Surface Mining Control and Reclamation Act of 1977 and similar state statutes, which require that mine property be restored in accordance with specified standards and an approved reclamation plan. The required reclamation activities to be performed are outlined in the Company's mining permits. These activities include reclaiming the pit and support acreage at surface mines, sealing portals at underground mines, and reclaiming refuse areas and slurry ponds.
	The following table describes the changes to the Company's asset retirement obligation liability:
		Year Ended December 31,
		2013			2012
		(In thousands)
	Balance at January 1 (including current portion)	$	448,625		$	473,903
	Accretion expense	35,727			39,020
	Obligations of divested operations	(8,440		)	—
	Adjustments to the liability from changes in estimates	(26,578		)	4,400
	Liabilities settled	(21,681		)	(68,698		)
	Balance at December 31	$	427,653		$	448,625
	Current portion included in accrued expenses	(24,940		)	(38,920		)
	Noncurrent liability	$	402,713		$	409,705
	During the year ended December 31, 2012, reclamation activities were accelerated, primarily at the Black Thunder mining complex, as employees and equipment impacted by market- related mine production cutbacks were redirected to reclamation activities.
	As of December 31, 2013, the Company had $247.3 million in surety bonds outstanding, $417.6 million in self-bonding, and $18.1 million in letters of credit to secure reclamation bonding obligations.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2013
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 available-for-sale equity securities, U.S. Treasury securities, and coal 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 and commodity contracts (coal and heating oil) 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 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 December 31, 2013.
	The table below sets forth, by level, the Company’s financial assets and liabilities that are recorded at fair value in the accompanying consolidated balance sheet:
		Fair Value at							31-Dec-13
		Total				Level 1				Level 2			Level 3
		(In thousands)
	Assets:
	Investments in marketable securities	$	264,443			$	77,967			$	186,476		$	—
	Derivatives	19,954				14,847				—			5,107
	Total assets	$	284,397			$	92,814			$	186,476		$	5,107
	Liabilities:
	Derivatives	$	12			$	—			$	(149	)	$	161
	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 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.
			Year Ended December 31,
			2013				2012
			(In thousands)
	Balance, beginning of period		$	8,174			$	6,211
	Realized and unrealized losses recognized in earnings, net		(10,253		)		(13,399		)
	Purchases		8,654				—
	Issuances		(25		)		17,312
	Settlements		(1,604		)		(1,950		)
	Ending balance		$	4,946			$	8,174
	Net unrealized losses of $2.5 million were recognized during the year ended December 31, 2013 related to level 3 financial instruments held on December 31, 2013 .
	Cash and Cash Equivalents
	At December 31, 2013 and 2012, the carrying amounts of cash and cash equivalents approximate their fair value.
	Fair Value of Long-Term Debt
	At December 31, 2013 and December 31, 2012, the fair value of the Company’s debt, including amounts classified as current, was $4.6 billion and $5.0 billion, 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.

Capital_Stock

Capital Stock	12 Months Ended
	Dec. 31, 2013
Capital Stock [Abstract]	'
Capital Stock	'
	Capital Stock
	On March 1, 2012, the Company filed a registration statement on Form S-3 with the SEC. The registration statement allows the Company to offer, from time to time, an unlimited amount of debt securities, preferred stock, depositary shares, purchase contracts, purchase units, common stock and related rights and warrants.
	Common Stock
	On June 8, 2011, the Company sold 48 million shares of its common stock at a public offering price of $27.00 per share. The $1.25 billion in net proceeds from the issuance were used to finance the acquisition of ICG. On July 8, 2011, the Company issued an additional 0.7 million shares of its common stock under the same terms and conditions to cover underwriters' over-allotments for net proceeds of $18.4 million.
	Stock Repurchase Plan
	The Company's share repurchase program allows for the purchase of up to 14,000,000 shares of the Company's common stock. At December 31, 2013, 10,925,800 shares of common stock were available for repurchase under the plan. There were no purchases made under the plan during the years ended December 31, 2013, 2012 and 2011. There is no expiration date on the program. Any future repurchases under the plan will be made at management's discretion and will depend on market conditions and other factors.

StockBased_Compensation_and_Ot

Stock-Based Compensation and Other Incentive Plans	12 Months Ended
	Dec. 31, 2013
Share-based Compensation [Abstract]	'
Stock-Based Compensation And Other Incentive Plans	'
	Stock-Based Compensation and Other Incentive Plans
	Under the Company's Stock Incentive Plan (the "Incentive Plan"), 30.9 million shares of the Company's common stock were reserved for awards to officers and other selected key management employees of the Company. The Incentive Plan provides the Board of Directors with the flexibility to grant stock options, stock appreciation rights, restricted stock awards, restricted stock units, performance stock or units, merit awards, phantom stock awards and rights to acquire stock through purchase under a stock purchase program ("Awards"). Awards the Board of Directors elects to pay out in cash do not impact the shares authorized in the Incentive Plan. Shares available for award under the plan were 10.3 million at December 31, 2013.
	Stock Options
	Stock options are granted at a strike price equal to the closing market price of the Company's common stock on the date of grant and are generally subject to vesting provisions of at least one year from the date of grant. Information regarding stock option activity under the Incentive Plan follows for the year ended December 31, 2013:
					Weighted Average			Aggregate				Average
		Common			Exercise			Intrinsic				Contract
		Shares			Price			Value				Life
		(In thousands)
	Options outstanding at January 1	5,215			$	25.89
	Granted	1,998			5.23
	Canceled	(138	)		29.01
	Expired	(136	)		31.57
	Options outstanding at December 31	6,939			19.86			$	3			6.7
	Options exercisable at December 31	3,724			28.14			—				5.3
	The aggregate intrinsic value of options exercised during the years ended December 31, 2012 and 2011 was $1.8 million and $2.6 million, respectively.
	Information regarding changes in stock options outstanding and not yet vested and the related grant-date fair value under the Incentive Plan follows for the year ended December 31, 2013:
				Weighted Average
		Common Shares		Grant-Date Fair Value
		(In thousands)
	Unvested options at January 1	2,369		$	7.72
	Granted	1,998		$	2.37
	Vested	-1,098		$	8.11
	Canceled	-53		$	3.97
	Unvested options at December 31	3,216		$	4.38
	Compensation expense related to stock options for the years ended December 31, 2013, 2012 and 2011 was $6.7 million, $8.0 million and $8.8 million, respectively. As of December 31, 2013, unrecognized compensation cost related to the unvested stock options totaled $4.9 million. The total grant-date fair value of options vested during the years ended December 31, 2013, 2012 and 2011 was $8.9 million, $8.0 million and $9.9 million, respectively. The options provide for the continuation of vesting for retirement-eligible recipients that meet certain criteria. The expense for these options is recognized through the date that the employee first becomes eligible to retire and is no longer required to provide service to earn part or all of the award. The majority of the cost relating to the stock-based compensation plans is included in "Selling, general and administrative expenses" in the accompanying consolidated statements of operations.
	Weighted average assumptions used in the Black-Scholes option pricing model for granted options follow:
		Year Ended December 31,
		2013				2012			2011
	Weighted average grant-date fair value per share of options granted	$	2.37			$	5.27		$	14.18
	Assumptions (weighted average):
	Risk-free interest rate	0.65%				0.76%			1.92%
	Expected dividend yield	2.30%				2.92%			1.25%
	Expected volatility	66.70%				60.70%			57.40%
	Expected life (in years)	4.5				4.5			4.5
	Expected volatilities are based on historical stock price movement and implied volatility from traded options on the Company's stock. The expected life of options is determined based on historical exercise activity. Most options granted vest over a period of three to four years.
	Restricted Stock and Restricted Stock Unit Awards
	The Company may issue restricted stock and restricted stock units, which require no payment from the employee. Restricted stock cliff-vests at various dates and restricted stock units ether vest ratably over or vest at the end of three years. Compensation expense is based on the fair value on the grant date and is recorded ratably over the vesting period. The employee receives cash compensation equal to the amount of dividends that would have been paid on the underlying shares.
	Information regarding restricted stock and restricted stock unit activity and weighted average grant-date fair value follows for the year ended December 31, 2013:
		Restricted Stock						Restricted Stock Units
					Weighted Average						Weighted Average
		Common			Grant-Date			Common			Grant-Date
		Shares			Fair Value			Shares			Fair Value
		(In thousands)						(In thousands)
	Outstanding at January 1	188			$	25.14		511			$	13.26
	Granted	—						969			5.2
	Vested	(44	)		17.3			(39	)		9.19
	Canceled	—			—			(19	)		7.21
	Outstanding at December 31	144			27.55			1,422			7.96
	Long-Term Incentive Compensation
	The Company has a long-term incentive program that allows for the award of performance units. The total number of units earned by a participant is based on financial and operational performance measures, and may be paid out in cash or in shares of the Company's common stock. The Company recognizes compensation expense over the three year term of the grant. The liabilities are remeasured quarterly. The Company recognized $9.1 million, $8.1 million and $2.7 million for the years ended December 31, 2013, 2012 and 2011, respectively. The expense is included primarily in "Selling, general and administrative expenses" in the accompanying consolidated statements of operations. Amounts accrued and unpaid for all grants under the plan totaled $17.2 million and $13.1 million as of December 31, 2013 and 2012, respectively.
	Deferred Compensation Plan
	The Company maintains a deferred compensation plan that allows eligible employees to defer receipt of compensation until the dates elected by the participant. Participants in the plan may defer up to 85% of their base salaries and up to 100% of their annual incentive awards. The plan also allows participants to defer receipt of up to 100% of the shares under any restricted stock unit or performance-contingent stock awards. The amounts deferred are invested in accounts that mirror the gains and losses of a number of different investment funds, including a hypothetical investment in shares of the Company's common stock. Participants are always vested in their deferrals to the plan and any related earnings. The Company has established a grantor trust to fund the obligations under the plan. The trust has purchased corporate-owned life insurance to offset these obligations. The net cash surrender values of the policies of $39.4 million and $35.4 million at December 31, 2013 and 2012 , respectively, are included in "Other noncurrent assets" in the accompanying consolidated balance sheets. The participants have an unsecured contractual commitment by the Company to pay the amounts due under the plan. Any assets placed in trust by the Company to fund future obligations of the plan are subject to the claims of creditors in the event of insolvency or bankruptcy, and participants are general creditors of the company as to their deferred compensation in the plans.
	Under the plan, the Company credits each participant's account with the number of units equal to the number of shares or units that the participant could purchase or receive with the amount of compensation deferred, based upon the fair market value of the underlying investment on that date. The amount the employee will receive from the plan will be based on the number of units credited to each participant's account, valued on the basis of the fair market value of an equivalent number of shares or units of the underlying investment on that date. The liability under the plan was $37.0 million and $31.3 million at December 31, 2013 and 2012.
	The Company's net income related to the deferred compensation plan for the years ended December 31, 2013, 2012 and 2011 was $2.6 million, $3.3 million and $6.2 million, respectively, most of which is included in "Selling, general and administrative expenses in the accompanying consolidated statements of operations.

Workers_Compensation_Expense

Workers' Compensation Expense	12 Months Ended
	Dec. 31, 2013
Workers' Compensation Expense [Abstract]	'
Workers' Compensation Expense	'
	Workers’ Compensation Expense
	The following table details the components of workers’ compensation expense:
				Year Ended December 31,
				2013				2012		2011
			(In thousands)
	Total occupational disease			6,137				6,962		3,365
	Traumatic injury claims and assessments			21,089				26,565		16,979
	Total workers’ compensation expense			$	27,226			$	33,527	$	20,344
	At December 31, 2013, accumulated gains of $0.9 million were not yet recognized in occupational disease cost and were recorded in accumulated other comprehensive income. Adjustments to the liability for curtailments of plan benefits were $0.8 in 2013 and $7.1 million in 2012.
	Summarized below is information about the amounts recognized in the accompanying consolidated balance sheets for workers' compensation benefits:
		December 31,
		2013				2012
		(In thousands)
	Occupational disease costs	$	55,228			$	58,431
	Traumatic and other workers' compensation claims	35,268				33,569
	Total obligations	90,496				92,000
	Less amount included in accrued expenses	12,434				10,371
	Noncurrent obligations	$	78,062			$	81,629
	As of December 31, 2013, the Company had $98.8 million in surety bonds and letters of credit outstanding to secure workers' compensation obligations.

Employee_Benefit_Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2013
Pension and Other Postretirement Benefit Expense [Abstract]	'
Employee Benefit Plans	'
	Employee Benefit Plans
	Defined Benefit Pension and Other Postretirement Benefit Plans
	The Company provides funded and unfunded non-contributory defined benefit pension plans covering certain of its salaried and hourly employees. Benefits are generally based on the employee's age and compensation. The Company funds the plans in an amount not less than the minimum statutory funding requirements or more than the maximum amount that can be deducted for U.S. federal income tax purposes.
	The Company also currently provides certain postretirement medical and life insurance coverage for eligible employees. Generally, covered employees who terminate employment after meeting eligibility requirements are eligible for postretirement coverage for themselves and their dependents. The salaried employee postretirement benefit plans are contributory, with retiree contributions adjusted annually, and contain other cost-sharing features such as deductibles and coinsurance. The Company's current funding policy is to fund the cost of all postretirement benefits as they are paid.
	Obligations and Funded Status.
	Summaries of the changes in the benefit obligations, plan assets and funded status of the plans are as follows:
										Other Postretirement
		Pension Benefits								Benefits
		2013				2012				2013				2012
		(In thousands)
	CHANGE IN BENEFIT OBLIGATIONS
	Benefit obligations at January 1	$	390,894			$	333,951			$	49,326			$	45,129
	Service cost	27,065				27,466				2,027				2,142
	Interest cost	16,207				15,668				1,739				2,020
	Plan amendments	—				—				—				2,183
	Benefits paid	(41,562		)		(23,624		)		(3,276		)		(4,244		)
	Curtailments	(3,027		)		(687		)		(2,519		)		(708		)
	Other-primarily actuarial loss (gain)	(34,109		)		38,120				(4,766		)		2,804
	Benefit obligations at December 31	$	355,468			$	390,894			$	42,531			$	49,326
	CHANGE IN PLAN ASSETS
	Value of plan assets at January 1	$	322,874			$	285,074			$	—			$	—
	Actual return on plan assets	52,247				42,396				—				—
	Employer contributions	14,393				19,028				3,276				4,244
	Benefits paid	(41,562		)		(23,624		)		(3,276		)		(4,244		)
	Value of plan assets at December 31	$	347,952			$	322,874			$	—			$	—
	Accrued benefit cost	$	(7,516	)		$	(68,020	)		$	(42,531	)		$	(49,326	)
	ITEMS NOT YET RECOGNIZED AS A COMPONENT OF NET PERIODIC BENEFIT COST
	Prior service credit (cost)	$	1,732			$	1,890			$	31,925			$	45,938
	Accumulated gain (loss)	10,096				(68,915		)		3,394				(1,531		)
		$	11,828			$	(67,025	)		$	35,319			$	44,407
	BALANCE SHEET AMOUNTS
	Current liability	$	(405	)		$	(390	)		$	(3,276	)		$	(4,240	)
	Noncurrent liability	$	(7,111	)		$	(67,630	)		$	(39,255	)		$	(45,086	)
		$	(7,516	)		$	(68,020	)		$	(42,531	)		$	(49,326	)
	Pension Benefits
	The accumulated benefit obligation for all pension plans was $341.1 million and $366.1 million at December 31, 2013 and 2012, respectively. The accumulated benefit obligation differs from the benefit obligation in that it includes no assumptions about future compensation levels.
	The benefit obligation and the accumulated benefit obligation for the Company's unfunded pension plan were $10.1 million and $8.8 million, respectively, at December 31, 2013.
	Prior service credit and net actuarial loss of $0.2 million and $3.8 million, respectively, will be amortized from accumulated other comprehensive income into net periodic benefit cost in 2014.
	Other Postretirement Benefits
	Prior service credit and net actuarial gain of $10.0 million and $0.7 million, respectively, will be amortized from accumulated other comprehensive income into net periodic benefit cost in 2014 .
	Components of Net Periodic Benefit Cost. The following table details the components of pension and postretirement benefit costs (credits):
														Other Postretirement
		Pension Benefits												Benefits
		Year Ended December 31,												Year Ended December 31,
		2013				2012				2011				2013				2012			2011
		(In thousands)
	Service cost	$	27,065			$	27,466			$	16,490			$	2,027			$	2,142		$	3,917
	Interest cost	16,207				15,668				16,253				1,739				2,020			3,279
	Curtailments	47				324				—				(5,444		)		(4,049		)	—
	Expected return on plan assets	(23,761		)		(22,030		)		(21,812		)		—				—			—
	Amortization of prior service credits	(204		)		259				(189		)		(10,621		)		(11,458		)	(2,364		)
	Amortization of other actuarial losses (gains)	14,616				14,666				8,748				(252		)		(522		)	(3,100		)
	Net benefit cost (credit)	$	33,970			$	36,353			$	19,490			$	(12,551	)		$	(11,867	)	$	1,732
	A curtailment was triggered in the third quarter of 2013 by reductions in employees' expected years of future service resulting primarily from the sale of Canyon Fuel.  Curtailments include the recognition of unamortized prior service costs and actuarial adjustments to the respective projected benefit obligations for the cash balance pension and medical plans and pneumoconiosis benefits.
	The differences generated from changes in assumed discount rates and returns on plan assets are amortized into earnings over a five-year period.
	Assumptions. The following table provides the assumptions used to determine the actuarial present value of projected benefit obligations at December 31.
		Pension Benefits				Other Postretirement Benefits
		2013		2012		2013		2012
	Weighted average assumptions:
	Discount rate	5.08%		4.13%		4.58%		3.64%
	Rate of compensation increase	3.39%		3.39%		N/A		N/A
	The following table provides the assumptions used to determine net periodic benefit cost for years ended December 31.
		Pension Benefits									Other Postretirement Benefits
	2013					2012		2011		2013				2012		2011
Weighted average assumptions:
Discount rate	4.13	%	/	5.05%		4.91%		5.71%		3.64%	/	4.58%		4.52%		5.23%
Rate of compensation increase	3.39%					3.39%		3.39%		N/A				N/A		N/A
Expected return on plan assets	7.75%					7.75%		8.50%		N/A				N/A		N/A
The Company establishes the expected long-term rate of return at the beginning of each fiscal year based upon historical returns and projected returns on the underlying mix of invested assets. The Company utilizes modern portfolio theory modeling techniques in the development of its return assumptions. This technique projects rates of return that can be generated through various asset allocations that lie within the risk tolerance set forth by members of the Company's pension committee (the "Pension Committee"). The risk assessment provides a link between a pension's risk capacity, management's willingness to accept investment risk and the asset allocation process, which ultimately leads to the return generated by the invested assets.
The health care cost trend rate assumed for 2014 is 7.3% and is expected to reach an ultimate trend rate of 4.5% by 2028. A one-percentage-point increase in the health care cost trend rate would have increased the postretirement benefit obligation at December 31, 2013 by $0.6 million. A one-percentage-point decrease in the health care cost trend rate would have decreased the postretirement benefit obligation at December 31, 2013 by $0.6 million. The effect of these changes would have had an insignificant impact on the net periodic postretirement benefit costs.
Plan Assets
The Pension Committee is responsible for overseeing the investment of pension plan assets. The Pension Committee is responsible for determining and monitoring appropriate asset allocations and for selecting or replacing investment managers, trustees and custodians. The pension plan's current investment targets are 65% equity and 35% fixed income securities. The Pension Committee reviews the actual asset allocation in light of these targets on a periodic basis and rebalances among investments as necessary. The Pension Committee evaluates the performance of investment managers as compared to the performance of specified benchmarks and peers and monitors the investment managers to ensure adherence to their stated investment style and to the plan's investment guidelines.
The Company's pension plan assets at December 31, 2013 and 2012, respectively, are categorized below according to the fair value hierarchy as defined in Note 16, "Fair Value Measurements":
	Total								Level 1								Level 2						Level 3
	2013				2012				2013				2012				2013			2012			2013		2012
	(In thousands)
Equity Securities:(A)
U.S. small-cap	$	14,901			$	13,099			$	14,901			$	13,099			$	—		$	—		$	—	$	—
U.S. mid-cap	62,271				43,946				28,654				12,717				33,617			31,229			—		—
U.S. large-cap	110,947				102,922				53,708				48,536				57,239			54,386			—		—
Non-U.S.	29,165				27,251				—				—				29,165			27,251			—		—
Fixed income securities:
U.S. government securities(B)	18,545				24,202				17,714				23,483				831			719			—		—
Non-U.S. government securities(C)	2,143				3,681				—				—				2,143			3,681			—		—
U.S. government asset and mortgage backed securities(D)	600				781				—				—				600			781			—		—
Corporate fixed income(E)	9,902				14,016				—				—				9,902			14,016			—		—
State and local government securities(F)	8,301				9,903				—				—				8,301			9,903			—		—
Other fixed income(G)	58,093				61,765				—				—				58,093			61,765			—		—
Short-term investments(H)	14,663				20,894				—				—				14,663			20,894			—		—
Other investments(I)	18,421				414				—				—				1,404			414			17,017		—
Total	$	347,952			$	322,874			$	114,977			$	97,835			$	215,958		$	225,039		$	17,017	$	—
(A) Equity securities includes investments in 1) common stock, 2) preferred stock and 3) mutual funds. Investments in common and preferred stocks are valued using quoted market prices multiplied by the number of shares owned. Investments in mutual funds are valued at the net asset value per share multiplied by the number of shares held as of the measurement date and are traded on listed exchanges.
(B) U.S. government securities includes agency and treasury debt. These investments are valued using dealer quotes in an active market.
(C) Non-U.S. government securities includes debt securities issued by foreign governments and are valued utilizing a price spread basis valuation technique with observable sources from investment dealers and research vendors.
(D) U.S. government asset and mortgage backed securities includes government-backed mortgage funds which are valued utilizing an income approach that includes various valuation techniques and sources such as discounted cash flows models, benchmark yields and securities, reported trades, issuer trades and/or other applicable data.
(E) Corporate fixed income is primarily comprised of corporate bonds and certain corporate asset-backed securities that are denominated in the U.S. dollar and are investment-grade securities. These investments are valued using dealer quotes.
(F) State and local government securities include different U.S. state and local municipal bonds and asset backed securities, these investments are valued utilizing a market approach that includes various valuation techniques and sources such as value generation models, broker quotes, benchmark yields and securities, reported trades, issuer trades and/or other applicable data.
(G) Other fixed income investments are actively managed fixed income vehicles that are valued at the net asset value per share multiplied by the number of shares held as of the measurement date.
(H) Short-term investments include governmental agency funds, government repurchase agreements, commingled funds, and pooled funds and mutual funds. Governmental agency funds are valued utilizing an option adjusted spread valuation technique and sources such as interest rate generation processes, benchmark yields and broker quotes. Investments in governmental repurchase agreements, commingled funds and pooled funds and mutual funds are valued at the net asset value per share multiplied by the number of shares held as of the measurement date.
(I) Other investments includes cash, forward contracts, derivative instruments, credit default swaps, interest rate swaps and mutual funds. Investments in interest rate swaps are valued utilizing a market approach that includes various valuation techniques and sources such as value generation models, broker quotes in active and non-active markets, benchmark yields and securities, reported trades, issuer trades and/or other applicable data. Forward contracts and derivative instruments are valued at their exchange listed price or broker quote in an active market. The mutual funds are valued at the net asset value per share multiplied by the number of shares held as of the measurement date and are traded on listed exchanges.
During 2013, the plan invested $16.0 million in Level 3 investments. Net unrealized gains from Level 3 investments were $1.0 million during 2013.
Cash Flows. The Company expects to make contributions of $4.0 million to the pension plans in 2014, which is impacted by the Moving Ahead for Progress in the 21st Century Act (MAP-21) enacted July 6, 2012. MAP-21 does not reduce the Company's obligations under the plan, but redistributes the timing of required payments by providing near term funding relief for sponsors under the Pension Protection Act.
The following represents expected future benefit payments from the plan, which reflect expected future service, as appropriate:
					Other
	Pension				Postretirement
	Benefits				Benefits
	(In thousands)
2014	$	21,844			$	4,020
2015	21,666				4,226
2016	27,689				4,415
2017	29,999				4,523
2018	33,488				4,602
Years 2019-2023	190,030				22,028
	$	324,716			$	43,814
Other Plans
The Company sponsors savings plans which were established to assist eligible employees provide for their future retirement needs. The Company's expense, representing its contributions to the plans, was $25.1 million, $27.2 million and $25.9 million for the years ended December 31, 2013, 2012 and 2011, respectively.

Earnings_Loss_Per_Common_Share

Earnings (Loss) Per Common Share	12 Months Ended
	Dec. 31, 2013
Earnings Per Share [Abstract]	'
Earnings (Loss) Per Common Share	'
	Earnings (Loss) Per Common Share
	In the year ended December 31, 2011, the dilutive impact of common stock equivalents under incentive plans was 0.8 million shares. The dilutive effects of 7.5 million, 4.9 million, and 2.6 million shares of common stock issuable under incentive plans were excluded from the calculation of diluted weighted average shares outstanding for the years ended December 31, 2013, 2012 and 2011, respectively, because the exercise price or grant price of the securities exceeded the average market price of the Company's common stock for these periods. The weighted average share impacts of options, restricted stock and restricted stock units that were excluded from the calculation of weighted average shares due to the Company's incurring a net loss for the years ended December 31, 2013 and 2012 were not significant.

Leases

Leases	12 Months Ended
	Dec. 31, 2013
Leases [Abstract]	'
Leases of Lessee Disclosure [Text Block]	'
	Leases
	The Company leases equipment, land and various other properties under non-cancelable long-term leases, expiring at various dates. Certain leases contain options that would allow the Company to extend the lease or purchase the leased asset at the end of the base lease term. In addition, the Company enters into various non-cancelable royalty lease agreements under which future minimum payments are due.
	Minimum payments due in future years under these agreements in effect at December 31, 2013 are as follows:
		Operating
		Leases		Royalties
		(In thousands)
	2014	$	31,532	$	17,394
	2015	24,466		19,143
	2016	16,851		21,070
	2017	14,509		20,806
	2018	3,739		22,255
	Thereafter	1,195		83,708
		$	92,292	$	184,376
	Rental expense, including amounts related to these operating leases and other shorter-term arrangements, amounted to $42.2 million in 2013, $41.2 million in 2012 and $43.9 million in 2011.
	Royalties are paid to lessors either as a fixed price per ton or as a percentage of the gross selling price of the mined coal. Royalties under the majority of the Company's significant leases are paid on the percentage of gross selling price basis. Royalty expense, including production royalties, was $261.1 million in 2013, $302.0 million in 2012 and $349.0 million in 2011.
	As of December 31, 2013, certain of the Company's lease obligations were secured by outstanding surety bonds totaling $55.4 million.

Risk_Concentrations

Risk Concentrations	12 Months Ended
	Dec. 31, 2013
Risks Concentrations [Abstract]	'
Concentration Risk Disclosure [Text Block]	'
	Risk Concentrations
	Credit Risk and Major Customers
	The Company has a formal written credit policy that establishes procedures to determine creditworthiness and credit limits for trade customers and counterparties in the over-the-counter coal market. Generally, credit is extended based on an evaluation of the customer's financial condition. Collateral is not generally required, unless credit cannot be established. Credit losses are provided for in the financial statements and historically have been minimal.
	The Company markets its steam coal principally to domestic and foreign electric utilities and its metallurgical coal to domestic and foreign steel producers. Revenues from export sales were $0.8 billion, $1.2 billion and $0.9 billion for the years ended December 31, 2013, 2012 and 2011, respectively. As of December 31, 2013 and 2012, accounts receivable from electric utilities totaled $125.7 million and $159.5 million, respectively, or 64% and 65% of total trade receivables, respectively. As of December 31, 2013 and 2012, accounts receivable from sales of metallurgical-quality coal totaled $70.5 million and $86.6 million, respectively, or 36% and 35%, of total trade receivables, respectively.
	The Company uses shipping destination as the basis for attributing revenue to individual countries. The Company's foreign revenues by geographical location are as follows:
		Year Ended December 31, 2013
		(In thousands)
	Europe (includes Morocco)	$	371,363
	Asia	160,404
	North America	80,322
	Central and South America	55,493
	Brokered Sales	154,442
	Total	$	822,024
	The Company is committed under long-term contracts to supply steam coal that meets certain quality requirements at specified prices. These prices are generally adjusted based on market indices. Quantities sold under some of these contracts may vary from year to year within certain limits at the option of the customer. The Company sold approximately 139.6 million tons of coal in 2013. Approximately 59% of this tonnage (representing approximately 49% of the Company's revenue) was sold under long-term contracts (contracts having a term of greater than one year). Long-term contracts range in remaining life from one to seven years.
	Third-party sources of coal
	The Company uses independent contractors to mine coal at certain mining complexes. The Company also purchases coal from third parties that it sells to customers. Factors beyond the Company's control could affect the availability of coal produced for or purchased by the Company. Disruptions in the quantities of coal produced for or purchased by the Company could impair its ability to fill customer orders or require it to purchase coal from other sources at prevailing market prices in order to satisfy those orders.
	Transportation
	The Company depends upon barge, rail, truck and belt transportation systems to deliver coal to its customers. Disruption of these transportation services due to weather-related problems, mechanical difficulties, strikes, lockouts, bottlenecks, and other events could temporarily impair the Company's ability to supply coal to its customers, resulting in decreased shipments. In the past, disruptions in rail service have resulted in missed shipments and production interruptions.

Settlement_with_Patriot_Coal

Settlement with Patriot Coal	12 Months Ended
	Dec. 31, 2013
Settlement with Patriot Coal [Abstract]	'
Legal Matters and Contingencies [Text Block]	'
	Settlement with Patriot Coal
	On December 31, 2005, Arch entered into a purchase and sale agreement to sell mining complexes to Magnum Coal Company ("Magnum"). On July 23, 2008, Patriot Coal Corporation acquired Magnum from Arc Light Capital Partners. On July 9, 2012, Patriot Coal Corporation and certain of its wholly owned subsidiaries, including Magnum, (collectively, "Patriot") filed voluntary petitions for reorganization under Chapter 11 of the U.S. Code in the U.S. Bankruptcy Court for the Southern District of New York.
	On October 4, 2013, we entered into a term sheet that was approved by the U.S. Bankruptcy Court on November 7, 2013, that resolves all pending and potential legal claims with Patriot stemming from the Company's sale of mining complexes to Magnum and the subsequent purchase of those companies by Patriot in 2008.
	The Company paid $5.0 million in cash to Patriot upon its exit from bankruptcy, which is reflected in "Other operating expense (income), net" in the consolidated statement of operations for the year ended December 31, 2013. Additionally, the settlement includes the release of a $16.7 million letter of credit posted by Patriot in the Company's favor for surety bonds related to the companies sold to Magnum. The Company also purchased Patriot's Guffey reserves for $16.0 million in cash upon their exit from bankruptcy. The Guffey reserves border the Company's Leer metallurgical coal complex.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Contingencies	'
	Commitments and Contingencies
	The Company accrues for cost 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.
	Allegheny Energy Supply (“Allegheny”), the sole customer of coal produced at the Company's subsidiary Wolf Run Mining Company's (“Wolf Run”) Sycamore No. 2 mine, filed a lawsuit against Wolf Run, Hunter Ridge Holdings, Inc. (“Hunter Ridge”), and ICG in state court in Allegheny County, Pennsylvania on December 28, 2006, and amended its complaint on April 23, 2007. Allegheny claimed that Wolf Run breached a coal supply contract when it declared force majeure under the contract upon idling the Sycamore No. 2 mine in the third quarter of 2006, and that Wolf Run continued to breach the contract by failing to ship in volumes referenced in the contract.  The Sycamore No. 2 mine was idled after encountering adverse geologic conditions and abandoned gas wells that were previously unidentified and unmapped.
	After extensive searching for gas wells and rehabilitation of the mine, it was re-opened in 2007, but with notice to Allegheny that it would necessarily operate at reduced volumes in order to safely and effectively avoid the many gas wells within the reserve.  The amended complaint also alleged that the production stoppages constitute a breach of the guarantee agreement by Hunter Ridge and breach of certain representations made upon entering into the contract in early 2005.  Allegheny voluntarily dropped the breach of representation claims later.  Allegheny claimed that it would incur costs in excess of $100 million to purchase replacement coal over the life of the contract.  ICG, Wolf Run and Hunter Ridge answered the amended complaint on August 13, 2007, disputing all of the remaining claims.
	On November 3, 2008, ICG, Wolf Run and Hunter Ridge filed an amended answer and counterclaim against the plaintiffs seeking to void the coal supply agreement due to, among other things, fraudulent inducement and conspiracy.  On September 23, 2009, Allegheny filed a second amended complaint alleging several alternative theories of liability in its effort to extend contractual liability to ICG, which was not a party to the original contract and did not exist at the time Wolf Run and Allegheny entered into the contract.  No new substantive claims were asserted.  ICG answered the second amended complaint on October 13, 2009, denying all of the new claims.  The Company's counterclaim was dismissed on motion for summary judgment entered on May 11, 2010.  Allegheny's claims against ICG were also dismissed by summary judgment, but the claims against Wolf Run and Hunter Ridge were not.  The court conducted a non-jury trial of this matter beginning on January 10, 2011 and concluding on February 1, 2011.
	At the trial, Allegheny presented its evidence for breach of contract and claimed that it is entitled to past and future damages in the aggregate of between $228 million and $377 million.  Wolf Run and Hunter Ridge presented their defense of the claims, including evidence with respect to the existence of force majeure conditions and excuse under the contract and applicable law.  Wolf Run and Hunter Ridge presented evidence that Allegheny's damages calculations were significantly inflated because it did not seek to determine damages as of the time of the breach and in some instances artificially assumed future nondelivery or did not take into account the apparent requirement to supply coal in the future.  On May 2, 2011, the trial court entered a Memorandum and Verdict determining that Wolf Run had breached the coal supply contract and that the performance shortfall was not excused by force majeure.  The trial court awarded total damages and interest in the amount of $104.1 million, which consisted of $13.8 million for past damages, and $90.3 million for future damages.  ICG and Allegheny filed post-verdict motions in the trial court and on August 23, 2011, the court denied the parties' motions.  The court entered a final judgment on August 25, 2011, in the amount of $104.1 million, which included pre-judgment interest.
	The parties appealed the lower court's decision to the Superior Court of Pennsylvania.  On August 13, 2012, the Superior Court of Pennsylvania affirmed the award of past damages, but ruled that the lower court should have calculated future damages as of the date of breach, and remanded the matter back to the lower court with instructions to recalculate that portion of the award. On November 19, 2012, Allegheny filed a Petition for Allowance of Appeal with the Supreme Court of Pennsylvania and Wolf Run and Hunter Ridge filed an Answer. On July 2, 2013, the Supreme Court of Pennsylvania denied the Petition of Allowance. As this action finalized the past damage award, Wolf Run paid $15.6 million for the past damage amount, including interest, to Allegheny in July 2013. The future damage award is now back before the lower court, and a new trial has been scheduled to start May 13, 2014.
	In addition, the Company is a party to numerous claims and lawsuits with respect to various matters. As of December 31, 2013 and December 31, 2012, the Company had accrued $30.4 million and $32.8 million, respectively, for all legal matters, including $11.7 million and $4.4 million, respectively, 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.
	The Company has unconditional purchase obligations relating to purchases of coal, materials and supplies and capital commitments, other than reserve acquisitions, and is also a party to transportation capacity commitments. The future commitments under these agreements total $293.0 million in 2014, $145.8 million in 2015, $111.3 million in 2016, $105.7 million in 2017, $80.8 million in 2018 and $407.7 million thereafter. During the years ended December 31, 2013, 2012 and 2011, the Company fulfilled its commitments under agreements containing unconditional obligations.

Segment_Information

Segment Information	12 Months Ended
	Dec. 31, 2013
Segment Reporting [Abstract]	'
Segment Reporting Disclosure [Text Block]	'
	Segment Information
	The Company's reportable business segments are based on the major coal producing basins in which the Company operates and may include a number of mine complexes. The Company manages its coal sales by coal basin, not by individual mining complex. Geology, coal transportation routes to customers, regulatory environments and coal quality or type are characteristic to a basin, and, accordingly, market and contract pricing have developed by coal basin. Mining operations are evaluated based on their per-ton operating costs (defined as including all mining costs but excluding pass-through transportation expenses), as well as on other non-financial measures, such as safety and environmental performance. The Company’s reportable segments are the Powder River Basin (PRB) segment, with operations in Wyoming; and the Appalachia (APP) segment, with operations in West Virginia, Kentucky, Maryland and Virginia.  The “Other” category combines other operating segments and includes the Company’s coal mining operations in Colorado and Illinois and our ADDCAR subsidiary.
	Operating segment results for the years ended December 31, 2013, 2012 and 2011 are presented below. Results for the reportable segments include all direct costs of mining, including all depreciation, depletion and amortization related to the mining operations, even if the assets are not recorded at the operating segment level. These reportable segments results do not reflect the mine closure or impairment costs, since those are not reflected in the operating income reviewed by management. Corporate, Other and Eliminations includes these charges, as well as the change in fair value of coal derivatives and coal trading activities, net; corporate overhead; land management; other support functions; and the elimination of intercompany transactions. The operating segment results reflect only those from continuing operations, and exclude the results of Canyon Fuel, since they are classified as discontinued operations in the consolidated statements of operations.
	The asset amounts below represent an allocation of assets consistent with the basis used for the Company’s incentive compensation plans. The amounts in Corporate, Other and Eliminations represent primarily corporate assets (cash, receivables, investments, plant, property and equipment) as well as unassigned coal reserves, above-market acquired sales contracts and other unassigned assets. Goodwill is allocated to the respective reporting units, even though it may not be reflected in the subsidiaries’ financial statements. Asset balances as of December 31, 2012 and 2011 include the assets of Canyon Fuel. Prior year asset amounts have been restated to reflect a change in how certain unassigned coal reserves and goodwill amounts are presented.
			PRB			APP				Other			Corporate,			Consolidated
										Operating			Other and
										Segments			Eliminations
			(in thousands)
	Year Ended December 31,	2013
	Revenues		$	1,482,813		$	1,145,800			$	385,744		$	—		$	3,014,357
	Income (loss) from operations		41,543			(108,387		)		64,943			(661,240		)	(663,141		)
	Depreciation, depletion and amortization		171,324			202,952				45,741			6,425			426,442
	Amortization of acquired sales contracts, net		(3,656		)	(10,364		)		4,563			—			(9,457		)
	Total assets		1,841,835			3,971,764				402,922			2,773,672			8,990,193
	Capital expenditures		9,784			167,759				23,122			96,319			296,984
	Year Ended December 31,	2012
	Revenues		$	1,524,536		$	1,793,576			$	450,014		$	—		$	3,768,126
	Income (loss) from operations		100,679			(606,235		)		74,142			(325,598		)	(757,012		)
	Depreciation, depletion and amortization		166,539			271,220				49,911			4,541			492,211
	Amortization of acquired sales contracts, net		(1,987		)	(23,926		)		724			—			(25,189		)
	Total assets		1,972,522			3,875,105				834,287			3,324,863			10,006,777
	Capital expenditures		23,410			275,476				68,220			28,119			395,225
	Year Ended December 31,	2011
	Revenues		$	1,646,947		$	1,915,090			$	321,002		$	—		$	3,883,039
	Income (loss) from operations		180,730			283,404				44,465			(165,538		)	343,061
	Depreciation, depletion and amortization		171,693			203,759				43,504			2,024			420,980
	Amortization of acquired sales contracts, net		19,458			(39,988		)		(1,539		)	—			(22,069		)
	Total assets		2,307,783			4,740,723				1,262,433			1,903,020			10,213,959
	Capital expenditures		110,999			217,435				94,599			117,903			540,936
	A reconciliation of segment income (loss) from operations to consolidated loss before income taxes follows:
			Year Ended December 31,
			2013			2012			2011
	Loss from operations		$	(663,141	)	$	(757,012	)	$	343,061
	Interest expense		(381,267		)	(317,615		)	(230,186		)
	Interest and investment income		6,603			5,473			3,309
	Nonoperating expense		(42,921		)	(23,668		)	(51,448		)
	Loss from continuing operations before income taxes		$	(1,080,726	)	$	(1,092,822	)	$	64,736

Quarterly_Financial_Informatio

Quarterly Financial Information	12 Months Ended
	Dec. 31, 2013
Quarterly Financial Information [Abstract]	'
Quarterly Financial Information [Text Block]	'
	Quarterly Selected Financial Data
	Quarterly selected financial data for the years ended December 31, 2013 and 2012 is summarized below:
		31-Mar			30-Jun			30-Sep			31-Dec
		(b)			(a)			(a) (b)			(a) (b)
		(In thousands, except per share data)
	2013:00:00
	Revenues	$	737,370		$	766,332		$	791,269		$	719,386
	Gross profit (loss)	$	(18,560	)	$	2,505		$	90		$	(44,801	)
	Asset impairment and mine closure costs	$	—		$	20,482		$	200,397		$	—
	Goodwill impairment	$	—		$	—		$	—		$	265,423
	Loss from operations	$	(51,431	)	$	(36,279	)	$	(234,753	)	$	(340,678	)
	Loss from continuing operations	$	(84,316	)	$	(80,351	)	$	(207,767	)	$	(372,794	)
	Income from discontinued operations, net of tax	$	14,267		$	8,145		$	79,404		$	1,580
	Net loss	$	(70,049	)	$	(72,206	)	$	(128,363	)	$	(371,214	)
	Diluted loss per common share
	Loss from continuing operations	$	(0.40	)	$	(0.38	)	$	(0.98	)	$	(1.76	)
	Net loss attributable to Arch Coal, Inc.	$	(0.33	)	$	(0.34	)	$	(0.61	)	$	(1.75	)
		31-Mar			30-Jun			30-Sep			31-Dec
		(b)			(a)			(a)			(a)
		(In thousands, except per share data)
	2012:00:00
	Revenues	$	960,237		$	965,685		$	975,170		$	867,034
	Gross profit	$	37,715		$	47,163		$	53,017		$	12,516
	Asset impairment and mine closure costs	$	—		$	525,583		$	(2,144	)	$	15,743
	Goodwill impairment	$	—		$	115,791		$	—		$	214,889
	Income (loss) from operations	$	27,797		$	(596,893	)	$	119,242		$	(307,158	)
	Income (loss) from continuing operations	$	(14,099	)	$	(442,456	)	$	24,673		$	(307,033	)
	Income from discontinued operations, net of tax	$	15,508		$	7,032		$	21,078		$	11,610
	Net income (loss)	$	1,409		$	(435,424	)	$	45,751		$	(295,423	)
	Diluted income (loss) per common share
	Income (loss) from continuing operations	$	(0.07	)	$	(2.09	)	$	0.12		$	(1.45	)
	Net loss attributable to Arch Coal, Inc.	$	0.01		$	(2.05	)	$	0.22		$	(1.39	)
	(a) In response to challenging market conditions, the Company made the decision to close or idle 10 mines in Appalachia and curtailed production at other thermal mines in the second quarter of 2012. Challenging markets also resulted in impairment charges relating to mining and other operations, investments in equity method subsidiaries and goodwill in both 2013 and 2012. See further discussion in Note 5, "Impairment Charges and Mine Closure Costs " and Note 6, "Goodwill ".
	(b) The Company entered into a definitive agreement on June 27, 2013 to sell Canyon Fuel and the sale was completed on August 16, 2013. Beginning in the second quarter of 2013, all quarterly filings with the Securities and Exchange Commission reflected Canyon Fuel as a discontinued operation in the consolidated statements of operations. These first quarter of 2013 and 2012 results reflect this presentation. See further information in Note 3, "Discontinued Operations".

Supplemental_Consolidating_Fin

Supplemental Consolidating Financial Information	12 Months Ended
	Dec. 31, 2013
Supplemental Condensed Consolidating Financial Information [Abstract]	'
Supplemental Condensed Consolidating Financial Information Text Block	'
	Supplemental Consolidating Financial Information
	Pursuant to the indentures governing Arch Coal, Inc.’s senior notes, certain wholly-owned subsidiaries of the Company have fully and unconditionally guaranteed the senior notes on a joint and several basis. The following tables present consolidating financial information for (i) the Company, (ii) the issuer of the senior notes, (iii) the guarantors under the senior notes, and (iv) the entities which are not guarantors under the senior notes (Arch Receivable Company, LLC and the Company’s subsidiaries outside the United States):
	Condensed Consolidating Statements of Operations and Comprehensive Income
	Year Ended December 31, 2013
		Parent/Issuer			Guarantor			Non-			Eliminations			Consolidated
					Subsidiaries			Guarantor
								Subsidiaries
		(In thousands)
	Revenues	$	—		$	3,014,357		$	—		$	—		$	3,014,357
	Costs, expenses and other
	Cost of sales (exclusive of items shown separately below)	9,117			2,657,583			—			(3,564		)	2,663,136
	Depreciation, depletion and amortization	5,949			420,458			35			—			426,442
	Amortization of acquired sales contracts, net	—			(9,457		)	—			—			(9,457		)
	Change in fair value of coal derivatives and coal trading activities, net	—			7,845			—			—			7,845
	Asset impairment and mine closure costs	78,150			142,729			—			—			220,879
	Goodwill impairment	—			265,423			—			—			265,423
	Selling, general and administrative expenses	88,820			39,825			7,038			(2,235		)	133,448
	Other operating income, net	4,209			(34,856		)	(5,370		)	5,799			(30,218		)
		186,245			3,489,550			1,703			—			3,677,498
	Loss from investment in subsidiaries	(328,889		)	—			—			328,889			—
	Loss from operations	(515,134		)	(475,193		)	(1,703		)	328,889			(663,141		)
	Interest expense, net
	Interest expense	(449,614		)	(24,747		)	(4,214		)	97,308			(381,267		)
	Interest and investment income	30,285			68,248			5,378			(97,308		)	6,603
		(419,329		)	43,501			1,164			—			(374,664		)
	Net loss resulting from early retirement and refinancing of debt	(42,921		)	—			—			—			(42,921		)
	Loss from continuing operations before income taxes	(977,384		)	(431,692		)	(539		)	328,889			(1,080,726		)
	Provision for (benefit from) income taxes	(335,552		)	—			54			—			(335,498		)
	Loss from continuing operations	(641,832		)	(431,692		)	(593		)	328,889			(745,228		)
	Income from discontinued operations, including gain on sale - net of tax	—			103,396			—			—			103,396
	Net loss	$	(641,832	)	$	(328,296	)	$	(593	)	$	328,889		$	(641,832	)
	Total comprehensive loss	$	(587,633	)	$	(304,278	)	$	(593	)	$	304,871		$	(587,633	)
	Condensed Consolidating Statements of Operations and Comprehensive Income
	Year Ended December 31, 2012
		Parent/Issuer			Guarantor			Non-			Eliminations			Consolidated
					Subsidiaries			Guarantor
								Subsidiaries
		(In thousands)
	Revenues	$	—		$	3,768,126		$	—		$	—		$	3,768,126
	Costs, expenses and other													—
	Cost of sales (exclusive of items shown separately below)	10,921			3,144,178			—			—			3,155,099
	Depreciation, depletion and amortization	5,392			486,786			33			—			492,211
	Amortization of acquired sales contracts, net	—			(25,189		)	—			—			(25,189		)
	Change in fair value of coal derivatives and coal trading activities, net	—			(16,590		)	—			—			(16,590		)
	Asset impairment and mine closure costs	—			539,182			—			—			539,182
	Goodwill impairment	—			330,680			—			—			330,680
	Contract settlement resulting from Patriot Coal bankruptcy	—			58,335			—			—			58,335
	Reduction in accrual related to acquired litigation	—			(79,532		)	—			—			(79,532		)
	Selling, general and administrative expenses	84,199			44,363			8,785			(3,048		)	134,299
	Other operating income, net	(13,392		)	(39,209		)	(13,804		)	3,048			(63,357		)
		87,120			4,443,004			(4,986		)	—			4,525,138
	Loss from investment in subsidiaries	(589,665		)	—			—			589,665			—
	Income (loss) from operations	(676,785		)	(674,878		)	4,986			589,665			(757,012		)
	Interest expense, net
	Interest expense	(366,584		)	(34,849		)	(3,221		)	87,039			(317,615		)
	Interest and investment income	27,750			57,268			7,494			(87,039		)	5,473
		(338,834		)	22,419			4,273			—			(312,142		)
	Other non-operating expense
	Net loss resulting from early retirement of debt	(21,975		)	(1,693		)	—			—			(23,668		)
	Income (loss) from continuing operations before income taxes	(1,037,594		)	(654,152		)	9,259			589,665			(1,092,822		)
	Provision for (benefit from) income taxes	(353,907		)	—			—			—			(353,907		)
	Income (loss) from continuing operations	(683,687		)	(654,152		)	9,259			589,665			(738,915		)
	Income from discontinued operations, net of tax	—			55,228			—			—			55,228
Net Income (loss)	(683,687		)	(598,924		)	9,259			589,665			(683,687		)
Less: Net income attributable to noncontrolling interest	(268		)	—			—			—			(268		)
Net Income (loss) attributable to Arch Coal, Inc.	$	(683,955	)	$	(598,924	)	$	9,259		$	589,665		$	(683,955	)
Total comprehensive income (loss)	$	(692,239	)	$	(604,903	)	$	9,259		$	595,644		$	(692,239	)
Condensed Consolidating Statements of Operations and Comprehensive Income
Year Ended December 31, 2011
	Parent/Issuer			Guarantor			Non-			Eliminations			Consolidated
				Subsidiaries			Guarantor
							Subsidiaries
	(In thousands)
Revenues	$	—		$	3,883,039		$	—		$	—		$	3,883,039
Costs, expenses and other													—
Cost of sales (exclusive of items shown separately below)	22,929			2,957,425			—			—			2,980,354
Depreciation, depletion and amortization	2,876			418,104			—			—			420,980
Amortization of acquired sales contracts, net	—			(22,069		)	—			—			(22,069		)
Change in fair value of coal derivatives and coal trading activities, net	—			(2,907		)	—			—			(2,907		)
Asset impairment and mine closure costs	—			7,316			—			—			7,316
Acquisition and transition costs	47,360			—			—			—			47,360
Selling, general and administrative expenses	74,591			43,572			3,527			(2,634		)	119,056
Other operating income, net	(23,306		)	10,811			(251		)	2,634			(10,112		)
	124,450			3,412,252			3,276			—			3,539,978
Loss from investment in subsidiaries	532,757			—			—			(532,757		)	—
Income (loss) from operations	408,307			470,787			(3,276		)	(532,757		)	343,061
Interest expense, net
Interest expense	(256,191		)	(46,218		)	(2,224		)	74,447			(230,186		)
Interest and investment income	15,935			55,041			6,780			(74,447		)	3,309
	(240,256		)	8,823			4,556			—			(226,877		)
Nonoperating expense	(49,490		)	(1,958		)	—			—			(51,448		)
Income (loss) from continuing operations before income taxes	118,561			477,652			1,280			(532,757		)	64,736
Provision for (benefit from) income taxes	(24,279		)	—			—			—			(24,279		)
Income (loss) from continuing operations	142,840			477,652			1,280			(532,757		)	89,015
Income from discontinued operations, net of tax	—			53,825			—			—			53,825
Net Income (loss)	142,840			531,477			1,280			(532,757		)	142,840
Less: Net income attributable to noncontrolling interest	(1,157		)	—			—			—			(1,157		)
Net Income (loss) attributable to Arch Coal, Inc.	$	141,683		$	531,477		$	1,280		$	(532,757	)	$	141,683
Total comprehensive income (loss)	$	141,240		$	537,561		$	1,280		$	(538,841	)	$	141,240
Condensed Consolidating Balance Sheets
December 31, 2013
	Parent/Issuer			Guarantor			Non-Guarantor			Eliminations			Consolidated
				Subsidiaries			Subsidiaries
	(In thousands)
Assets
Cash and cash equivalents	$	799,333		$	100,418		$	11,348		$	—		$	911,099
Restricted cash	—			—			—			—			—
Short term investments	248,414			—			—			—			248,414
Receivables	14,177			23,018			197,015			(4,637		)	229,573
Inventories	—			264,161			—			—			264,161
Other	84,401			43,617			806			—			128,824
Total current assets	1,146,325			431,214			209,169			(4,637		)	1,782,071
Property, plant and equipment, net	24,851			6,709,398			37			—			6,734,286
Investment in subsidiaries	7,741,589			—			—			(7,741,589		)	—
Intercompany receivables				1,953,719			(181,095		)	(1,772,624		)	—
Note receivable from Arch Western	675,000			—			—			(675,000		)	—
Other	162,287			311,463			86			—			473,836
Total other assets	8,578,876			2,265,182			(181,009		)	(10,189,213		)	473,836
Total assets	$	9,750,052		$	9,405,794		$	28,197		$	(10,193,850	)	$	8,990,193
Liabilities and Stockholders’ Equity
Accounts payable	$	17,781		$	158,224		$	137		$	—		$	176,142
Accrued expenses and other current liabilities	53,779			228,664			781			(4,637		)	278,587
Current maturities of debt	28,882			4,611			—			—			33,493
Total current liabilities	100,442			391,499			918			(4,637		)	488,222
Long-term debt	5,099,833			18,169			—						5,118,002
Intercompany payables	1,772,624			—			—			(1,772,624		)	—
Note payable to Arch Coal	—			675,000			—			(675,000		)	—
Asset retirement obligations	1,095			401,618			—			—			402,713
Accrued pension benefits	7,797			(686		)	—			—			7,111
Accrued postretirement benefits other than pension	12,079			27,176			—			—			39,255
Accrued workers’ compensation	21,546			56,516			—			—			78,062
Deferred income taxes	413,546			—			—			—			413,546
Other noncurrent liabilities	67,841			121,794			398			—			190,033
Total liabilities	7,496,803			1,691,086			1,316			(2,452,261		)	6,736,944
Stockholders’ equity	2,253,249			7,714,708			26,881			(7,741,589		)	2,253,249
Total liabilities and stockholders’ equity	$	9,750,052		$	9,405,794		$	28,197		$	(10,193,850	)	$	8,990,193
Condensed Consolidating Balance Sheets
December 31, 2012
	Parent/Issuer			Guarantor			Non-Guarantor			Eliminations			Consolidated
				Subsidiaries			Subsidiaries
	(In thousands)
Assets
Cash and cash equivalents	$	671,313		$	100,468		$	12,841		$	—		$	784,622
Restricted cash	3,453			—			—			—			3,453
Short term investments	234,305			—			—			—			234,305
Receivables	49,281			40,452			247,171			(4,824		)	332,080
Inventories	—			365,424			—			—			365,424
Other	106,786			86,877			557			—			194,220
Total current assets	1,065,138			593,221			260,569			(4,824		)	1,914,104
Property, plant and equipment, net	27,476			7,309,550			72			—			7,337,098
Investment in subsidiaries	8,254,508			—			—			(8,254,508		)	—
Intercompany receivables	—			1,600,311			—			(1,600,311		)	—
Note receivable from Arch Western	675,000			—			—			(675,000		)	—
Other	187,171			568,314			90			—			755,575
Total other assets	9,116,679			2,168,625			90			(10,529,819		)	755,575
Total assets	$	10,209,293		$	10,071,396		$	260,731		$	(10,534,643	)	$	10,006,777
Liabilities and Stockholders’ Equity
Accounts payable	$	19,859		$	204,370		$	189		$	—		$	224,418
Accrued expenses and other current liabilities	65,293			259,162			124			(4,824		)	319,755
Current maturities of debt	32,054			842			—			—			32,896
Total current liabilities	117,206			464,374			313			(4,824		)	577,069
Long-term debt	5,061,925			23,954			—			—			5,085,879
Intercompany payables	1,367,739			—			232,572			(1,600,311		)	—
Note payable to Arch Coal	—			675,000			—			(675,000		)	—
Asset retirement obligations	1,646			408,059			—			—			409,705
Accrued pension benefits	33,456			34,174			—			—			67,630
Accrued postretirement benefits other than pension	13,953			31,133			—			—			45,086
Accrued workers’ compensation	25,323			56,306			—			—			81,629
Deferred income taxes	664,182			—			—			—			664,182
Other noncurrent liabilities	69,296			151,360			374			—			221,030
Total liabilities	7,354,726			1,844,360			233,259			(2,280,135		)	7,152,210
Stockholders’ equity	2,854,567			8,227,036			27,472			(8,254,508		)	2,854,567
Total liabilities and stockholders’ equity	$	10,209,293		$	10,071,396		$	260,731		$	(10,534,643	)	$	10,006,777
Condensed Consolidating Statements of Cash Flows
Year Ended December 31, 2013
	Parent/Issuer			Guarantor			Non-Guarantor			Eliminations			Consolidated
				Subsidiaries			Subsidiaries
	(In thousands)
Cash provided by (used in) operating activities	$	(632,060	)	$	637,193		$	50,609		$	—		$	55,742
Investing Activities
Capital expenditures	(3,320		)	(293,664		)	—			—			(296,984		)
Additions to prepaid royalties	—			(14,947		)	—			—			(14,947		)
Proceeds from dispositions of property, plant and equipment	—			10,790			—			—			10,790
Proceeds from sales-leaseback transactions	—			34,919			—			—			34,919
Proceeds from sale of Canyon Fuel	—			422,663			—			—			422,663
Purchases of short term investments	(213,726		)	—			—			—			(213,726		)
Proceeds from sales of short term investments	194,537			—			—			—			194,537
Investments in and advances to affiliates	(5,451		)	(10,321		)	—			512			(15,260		)
Change in restricted cash	3,453			—			—			—			3,453
Cash provided by (used in) investing activities	(24,507		)	149,440			—			512			125,445
Financing Activities
Contributions from parent	—			512			—			(512		)	—
Proceeds from term loan and senior notes	644,000			—			—			—			644,000
Payments to retire debt	(628,660		)	(512		)	—			—			(629,172		)
Payments on term loan	(17,250		)	—			—			—			(17,250		)
Net payments on other debt	(6,324		)	—			—			—			(6,324		)
Debt financing costs	(19,864		)	—			(625		)	—			(20,489		)
Dividends paid	(25,475		)	—			—			—			(25,475		)
Transactions with affiliates, net	838,160			(786,683		)	(51,477		)	—			—
Cash provided by (used in) financing activities	784,587			(786,683		)	(52,102		)	(512		)	(54,710		)
Increase (decrease) in cash and cash equivalents	128,020			(50		)	(1,493		)	—			126,477
Cash and cash equivalents, beginning of period	671,313			100,468			12,841			—			784,622
Cash and cash equivalents, end of period	$	799,333		$	100,418		$	11,348		$	—		$	911,099
Condensed Consolidating Statements of Cash Flows
Year Ended December 31, 2012
	Parent/Issuer			Guarantor			Non-Guarantor			Eliminations			Consolidated
				Subsidiaries			Subsidiaries
	(In thousands)
Cash provided by (used in) operating activities	$	(571,576	)	$	781,551		$	122,829		$	—		$	332,804
Investing Activities
Change in restricted cash	6,869			—			—			—			6,869
Capital expenditures	(4,424		)	(390,801		)	—			—			(395,225		)
Proceeds from dispositions of property, plant and equipment	—			1,328			21,497			—			22,825
Investments in and advances to affiliates	(6,287		)	(13,134		)	—			1,663			(17,758		)
Purchases of short term investments	(236,862		)	—			—			—			(236,862		)
Proceeds from sales of short term investments	1,754			—			—			—			1,754
Purchase of noncontrolling interest	(17,500		)	—			—			—			(17,500		)
Additions to prepaid royalties	—			(13,269		)	—			—			(13,269		)
Cash provided by (used in) investing activities	(256,450		)	(415,876		)	21,497			1,663			(649,166		)
Financing Activities
Contributions from parent	—			1,663			—			(1,663		)	—
Proceeds from term loan and senior notes	1,993,253			—			—			—			1,993,253
Payments to retire debt	—			(452,934		)	—			—			(452,934		)
Net decrease in borrowings under lines of credit and commercial paper program	(375,000		)	—			(106,300		)	—			(481,300		)
Payments on term loan	(7,625		)	—			—			—			(7,625		)
Net payments on other debt	(682		)	—			—			—			(682		)
Debt financing costs	(50,022		)	—			(546		)	—			(50,568		)
Dividends paid	(42,440		)	—			—			—			(42,440		)
Issuance of common stock under incentive plans	5,131			—			—			—			5,131
Transactions with affiliates, net	(84,651		)	110,639			(25,988		)	—			—
Cash provided by (used in) financing activities	1,437,964			(340,632		)	(132,834		)	(1,663		)	962,835
Increase in cash and cash equivalents	609,938			25,043			11,492			—			646,473
Cash and cash equivalents, beginning of period	61,375			75,425			1,349			—			138,149
Cash and cash equivalents, end of period	$	671,313		$	100,468		$	12,841		$	—		$	784,622
Condensed Consolidating Statements of Cash Flows
Year Ended December 31, 2011
	Parent/Issuer			Guarantor			Non-Guarantor			Eliminations			Consolidated
				Subsidiaries			Subsidiaries
	(In thousands)
Cash provided by (used in) operating activities	$	(187,039	)	$	998,082		$	(168,801	)	$	—		$	642,242
Investing Activities
Acquisition of ICG, net of cash acquired	(2,894,339		)	—			—			—			(2,894,339		)
Change in restricted cash	5,167			—			—			—			5,167
Capital expenditures	(12,809		)	(528,021		)	(106		)	—			(540,936		)
Proceeds from dispositions of property, plant and equipment	—			25,887			—			—			25,887
Investments in and advances to affiliates	(633,534		)	(33,553		)	—			605,178			(61,909		)
Additions to prepaid royalties	—			(29,957		)	—			—			(29,957		)
Consideration paid related to prior business acquisition	(829		)	—			—			—			(829		)
Cash provided by (used in) investing activities	(3,536,344		)	(565,644		)	(106		)	605,178			(3,496,916		)
Financing Activities
Contributions from parent	—			605,178			—			(605,178		)	—
Proceeds from the issuance of senior notes	2,000,000			—			—			—			2,000,000
Proceeds from the issuance of common stock, net	1,267,933			—			—			—			1,267,933
Payments to retire debt	—			(605,178		)	—			—			(605,178		)
Net decrease in borrowings under lines of credit and commercial paper program	375,000			(56,904		)	106,300			—			424,396
Net proceeds from other debt	5,334			—			—			—			5,334
Debt financing costs	(114,799		)	(16		)	(8		)	—			(114,823		)
Dividends paid	(80,748		)	—			—			—			(80,748		)
Issuance of common stock under incentive plans	2,316			—			—			—			2,316
Transactions with affiliates, net	316,009			(379,973		)	63,964			—			—
Cash provided by (used in) financing activities	3,771,045			(436,893		)	170,256			(605,178		)	2,899,230
Increase (decrease) in cash and cash equivalents	47,662			(4,455		)	1,349			—			44,556
Cash and cash equivalents, beginning of period	13,713			79,880			—			—			93,593
Cash and cash equivalents, end of period	$	61,375		$	75,425		$	1,349		$	—		$	138,149

Valuation_and_Qualifying_Accou

Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2013
Valuation and Qualifying Accounts [Abstract]	'
Valuation and Qualifying Accounts	'
	Valuation and Qualifying Accounts
				Additions
				(Reductions)
		Balance at		Charged to		Charged to						Balance at
		Beginning of		Costs and		Other						End of
		Year		Expenses		Accounts				Deductions (a)		Year
		(In thousands)
	Year ended December 31, 2013
	Reserves deducted from asset accounts:
	Other assets — other notes and accounts receivable	$	1,043	$	346	$	—			$	614	$	775
	Current assets — supplies and inventory	12,589		503		(2,274		)	(b)	2,372		8,446
	Deferred income taxes	34,663		8,659		—				—		43,322
	Year ended December 31, 2012
	Reserves deducted from asset accounts:
	Other assets — other notes and accounts receivable	$	17	$	1,039	$	—			$	13	$	1,043
	Current assets — supplies and inventory	13,107		1,961		—				2,479		12,589
	Deferred income taxes	2,831		31,832		—				—		34,663
	Year ended December 31, 2011
	Reserves deducted from asset accounts:
	Other assets — other notes and accounts receivable	$	—	$	17	$	—			$	—	$	17
	Current assets — supplies and inventory	12,701		1,755		—				1,349		13,107
	Deferred income taxes	737		2,416		—				322		2,831
	(a)     Reserves utilized, unless otherwise indicated.
	(b)    Disposition of subsidiaries

Basis_of_Presentation_Consolid

Basis of Presentation Consolidation Policy (Policies)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Consolidation, Policy [Policy Text Block]	'
	Basis of Presentation
	The accompanying consolidated financial statements include the accounts of Arch Coal, Inc. and its subsidiaries and controlled entities (the “Company”). 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, Kentucky, Maryland, Virginia, Illinois, Wyoming and Colorado. All subsidiaries are wholly-owned. Intercompany transactions and accounts have been eliminated in consolidation.
	The Company completed the sale of Canyon Fuel Company, LLC (Canyon Fuel) on August 16, 2013. The results of these mining complexes have been segregated from continuing operations and are reflected, net of tax, as discontinued operations in the consolidated statements of operations for all periods presented. See further discussion in Note 3, "Discontinued Operations".
	In response to decreasing demand for thermal coal in Appalachia, the Company closed four mining complexes, temporarily idled a fifth complex, and curtailed production at other mines in the Appalachia region in the second quarter of 2012. The results for the closed and idled complexes are reflected in income from continuing operations in the consolidated statements of operations. See further discussion in Note 5, "Impairment Charges and Mine Closure Costs".
	The Company's subsidiary Arch Western Resources, LLC (“Arch Western”) operates thermal coal mines in the western U.S. On April 9, 2012, Delta Housing, Inc., a subsidiary of BP p.l.c. and a joint venture partner in Arch Western, exercised their contractual right to require the Company to purchase their common and preferred membership interests in Arch Western.  With the payment of the negotiated purchase amount of $17.5 million on July 2, 2012, Arch Western became a wholly-owned subsidiary.

Accounting_Policies_Policies

Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Basis of Presentation	'
	Basis of Presentation
	The accompanying consolidated financial statements include the accounts of Arch Coal, Inc. and its subsidiaries and controlled entities (the “Company”). 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, Kentucky, Maryland, Virginia, Illinois, Wyoming and Colorado. All subsidiaries are wholly-owned. Intercompany transactions and accounts have been eliminated in consolidation.
	The Company completed the sale of Canyon Fuel Company, LLC (Canyon Fuel) on August 16, 2013. The results of these mining complexes have been segregated from continuing operations and are reflected, net of tax, as discontinued operations in the consolidated statements of operations for all periods presented. See further discussion in Note 3, "Discontinued Operations".
	In response to decreasing demand for thermal coal in Appalachia, the Company closed four mining complexes, temporarily idled a fifth complex, and curtailed production at other mines in the Appalachia region in the second quarter of 2012. The results for the closed and idled complexes are reflected in income from continuing operations in the consolidated statements of operations. See further discussion in Note 5, "Impairment Charges and Mine Closure Costs".
	The Company's subsidiary Arch Western Resources, LLC (“Arch Western”) operates thermal coal mines in the western U.S. On April 9, 2012, Delta Housing, Inc., a subsidiary of BP p.l.c. and a joint venture partner in Arch Western, exercised their contractual right to require the Company to purchase their common and preferred membership interests in Arch Western.  With the payment of the negotiated purchase amount of $17.5 million on July 2, 2012, Arch Western became a wholly-owned subsidiary.
Accounting Pronouncements Adopted And New Pronoucements Not Yet Implemented	'
	Accounting Pronouncements
	There are no accounting pronouncements whose adoption had, or is expected to have, a material impact on the Company's consolidated financial statements.
Accounting Estimates	'
	Accounting Estimates
	The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and revenues and expenses in the accompanying consolidated financial statements and the disclosure of contingent assets and liabilities. Actual results could differ from those estimates.
Cash and Cash Equivalents	'
	Cash and Cash Equivalents
	Cash and cash equivalents are stated at cost. Cash equivalents consist of highly-liquid investments with an original maturity of three months or less when purchased.
Allowance for Uncollectible Receivables	'
	Allowance for Uncollectible Receivables
	The Company establishes an allowance for uncollectible receivables for the amounts of trade accounts receivable and other receivables that are not expected to be collected, based on past collection history, the economic environment and specified risks identified in the receivables portfolio. Receivables are considered past due if the full payment is not received by the contractual due date. At December 31, 2013 and 2012, the allowance for uncollectible receivables was insignificant.
Inventories	'
	Inventories
	Coal and supplies inventories are valued at the lower of average cost or market. Coal inventory costs include labor, supplies, equipment costs, transportation costs incurred prior to the transfer of title to customers and operating overhead. The costs of removing overburden, called stripping costs, incurred during the production phase of the mine are considered variable production costs and are included in the cost of the coal extracted during the period the stripping costs are incurred.
Investments and Membership Interests in Joint Ventures	'
	Investments and Membership Interests in Joint Ventures
	Investments and membership interests in joint ventures are accounted for under the equity method of accounting if the Company has the ability to exercise significant influence, but not control, over the entity. The Company's share of the entity's income or loss is reflected in "Other operating expense (income), net" in the consolidated statements of operations. Information about investment activity is provided in Note 9, " Equity Method Investments and Membership Interests in Joint Ventures"
	Investments in debt securities and marketable equity securities that do not qualify for equity method accounting are classified as available-for-sale and are recorded at their fair values. Unrealized gains and losses on these investments are recorded in other comprehensive income or loss. A decline in the value of an investment that is considered other-than-temporary would be recognized in operating expenses.
Prepaid Royalties	'
	Prepaid Royalties
	Leased mineral rights are often acquired through royalty payments. When royalty payments represent prepayments recoupable against future production, they are recorded as a prepaid asset, with amounts expected to be recouped within one year classified as current. When the coal is mined under these leases the royalties are recouped and the prepayment is charged to cost of sales.
Acquired Sales Contracts	'
	Acquired Sales Contracts
	Coal supply agreements (sales contracts) acquired in a business combination are capitalized at their fair value and amortized over the tons of coal shipped during the term of the contract. The fair value of a sales contract is determined by discounting the cash flows attributable to the difference between the contract price and the prevailing forward prices for the tons under contract at the date of acquisition. See Note 10, "Acquired Sales Contracts" for further information related to the Company's acquired sales contracts.
Exploration Costs	'
	Exploration Costs
	Costs to acquire permits for exploration activities are capitalized. Drilling and other costs related to locating coal deposits and evaluating the economic viability of such deposits are expensed as incurred.
Property, Plant and Equipment	'
	Property, Plant and Equipment
	Plant and Equipment
	Plant and equipment are recorded at cost. Interest costs incurred during the construction period for major asset additions are capitalized. We capitalized $15.9 million, $15.6 million, and $1.9 million of interest costs during the years ended December 31, 2013, 2012, and 2011, respectively. Expenditures that extend the useful lives of existing plant and equipment or increase the productivity of the asset are capitalized. The cost of maintenance and repairs that do not extend the useful life or increase the productivity of the asset are expensed as incurred.
	Preparation plants and loadouts are depreciated using the units-of-production method over the estimated recoverable reserves, subject to a minimum level of depreciation. Other plant and equipment are depreciated principally using the straight-line method over the estimated useful lives of the assets, limited by the remaining life of the mine. The useful lives of mining equipment, including longwalls, draglines and shovels, range from 5 to 32 years. The useful lives of buildings and leasehold improvements generally range from 10 to 30 years.
	Deferred Mine Development
	Costs of developing new mines or significantly expanding the capacity of existing mines are capitalized and amortized using the units-of-production method over the estimated recoverable reserves that are associated with the property being benefited. Costs may include construction permits and licenses; mine design; construction of access roads, shafts, slopes and main entries; and removing overburden to access reserves in a new pit. Additionally, deferred mine development includes the asset cost associated with asset retirement obligations.
	Coal Lands and Mineral Rights
	Rights to coal reserves may be acquired directly through governmental or private entities. A significant portion of the Company's coal reserves are controlled through leasing arrangements. Lease agreements are generally long-term in nature (original terms range from 10 to 50 years), and substantially all of the leases contain provisions that allow for automatic extension of the lease term providing certain requirements are met.
	The net book value of the Company's coal interests was $4.8 billion and $5.1 billion at December 31, 2013 and 2012. Payments to acquire royalty lease agreements and lease bonus payments are capitalized as a cost of the underlying mineral reserves and depleted over the life of proven and probable reserves. Coal lease rights are depleted using the units-of-production method, and the rights are assumed to have no residual value.
	Future lease bonus payments total $60.4 million in 2014, $75.8 million in 2015, $60.4 million in 2016, and $0.4 million in 2017.
	Depreciation, depletion and amortization.
	The depreciation, depletion and amortization related to long-lived assets is reflected in the statement of operations as a separate line item. No depreciation, depletion or amortization is included in any other operating cost categories.
	Impairment
	If facts and circumstances suggest that the carrying value of a long-lived asset or asset group may not be recoverable, the asset or asset group is reviewed for potential impairment. If this review indicates that the carrying amount of the asset will not be recoverable through projected undiscounted cash flows generated by the asset and its related asset group over its remaining life, then an impairment loss is recognized by reducing the carrying value of the asset to its fair value. The Company may, under certain circumstances, idle mining operations in response to market conditions or other factors. Because an idling is not a permanent closure, it is not considered an automatic indicator of impairment.
Goodwill	'
	Goodwill
	In a business combination, goodwill represents the excess of the purchase price over the fair value assigned to the net tangible and identifiable intangible assets acquired. The Company tests goodwill for impairment annually as of the beginning of the fourth quarter, or when circumstances indicate a possible impairment may exist. If the results of the testing indicate that the carrying amount of a reporting unit exceeds the fair value of the reporting unit, the fair value of goodwill must be calculated. An impairment loss generally would be recognized when the carrying amount of goodwill exceeds the implied fair value of goodwill, determined by subtracting the fair value of the other assets and liabilities associated with the reporting unit from the total fair value of the reporting unit. The fair value of a reporting unit is determined using a discounted cash flow ("DCF") technique. A number of significant assumptions and estimates are involved in the application of the DCF analysis to forecast operating cash flows, including the discount rate, projections of production volumes, quality and costs to produce; projections of sales volumes by market (e.g., thermal versus metallurgical); and projections of market prices. See additional discussion in Note 6, "Goodwill."
Deferred Financing Costs	'
	Deferred Financing Costs
	The Company capitalizes costs incurred in connection with new borrowings, the establishment or enhancement of credit facilities and the issuance of debt securities. These costs are amortized as an adjustment to interest expense over the life of the borrowing or term of the credit facility using the interest method. The unamortized balance of deferred financing costs was $99.2 million and $101.5 million at December 31, 2013 and 2012, respectively. Amounts classified as current were $19.7 million and $17.3 million at December 31, 2013 and 2012, respectively. Current amounts are recorded in "Other current assets" and noncurrent amounts are recorded in "Other noncurrent assets" in the accompanying consolidated balance sheets.
Revenue Recognition	'
	Revenue Recognition
	Revenues include sales to customers of coal produced at Company operations and coal purchased from third parties. The Company recognizes revenue at the time risk of loss passes to the customer at contracted amounts. Transportation costs are included in cost of sales and amounts billed by the Company to its customers for transportation are included in revenues.
Other Operating Income, Net	'
	Other operating expense (income), net in the accompanying consolidated statements of operations reflects income and expense from sources other than physical coal sales, including: bookouts, the practice of offsetting purchase and sale contracts for shipping convenience purposes, and contract settlements; royalties earned from properties leased to third parties; income from equity investments; gains and losses from dispositions of assets; and realized gains and losses on heating oil derivatives that do not qualify for hedge accounting and are not held for trading purposes.
Asset Retirement Obligations	'
	Asset Retirement Obligations
	The Company's legal obligations associated with the retirement of long-lived assets are recognized at fair value at the time the obligations are incurred. Accretion expense is recognized through the expected settlement date of the obligation. Obligations are incurred at the time development of a mine commences for underground and surface mines or construction begins for support facilities, refuse areas and slurry ponds. The obligation's fair value is determined using a DCF technique and is based upon permit requirements and various estimates and assumptions that would be used by market participants, including estimates of disturbed acreage, reclamation costs and assumptions regarding equipment productivity. Upon initial recognition of a liability, a corresponding amount is capitalized as part of the carrying value of the related long-lived asset.
	The Company reviews its asset retirement obligation at least annually and makes necessary adjustments for permit changes as granted by state authorities and for revisions of estimates of the amount and timing of costs. For ongoing operations, adjustments to the liability result in an adjustment to the corresponding asset. For idle operations, adjustments to the liability are recognized as income or expense in the period the adjustment is recorded. Any difference between the recorded obligation and the actual cost of reclamation is recorded in profit or loss in the period the obligation is settled. See additional discussion in Note 15, "Asset Retirement Obligations."
Derivative Instruments	'
	Derivative Instruments
	The Company generally utilizes derivative instruments to manage exposures to commodity prices. Additionally, the Company may hold certain coal derivative instruments for trading purposes. Derivative financial instruments are recognized in the balance sheet at fair value. Certain coal contracts may meet the definition of a derivative instrument, but because they provide for the physical purchase or sale of coal in quantities expected to be used or sold by the Company over a reasonable period in the normal course of business, they are not recognized on the balance sheet.
	Certain derivative instruments are designated as the hedge instrument in a hedging relationship. In a fair value hedge, the Company hedges the risk of changes in the fair value of a firm commitment, typically a fixed-price coal sales contract. Changes in both the hedged firm commitment and the fair value of a derivative used as a hedge instrument in a fair value hedge are recorded in earnings. In a cash flow hedge, the Company hedges the risk of changes in future cash flows related to a forecasted purchase or sale. Changes in the fair value of the derivative instrument used as a hedge instrument in a cash flow hedge are recorded in other comprehensive income or loss. Amounts in other comprehensive income or loss are reclassified to earnings when the hedged transaction affects earnings and are classified in a manner consistent with the transaction being hedged. The Company formally documents the relationships between hedging instruments and the respective hedged items, as well as its risk management objectives for hedge transactions.
	The Company evaluates the effectiveness of its hedging relationships both at the hedge's inception and on an ongoing basis. Any ineffective portion of the change in fair value of a derivative instrument used as a hedge instrument in a fair value or cash flow hedge is recognized immediately in earnings. The ineffective portion is based on the extent to which exact offset is not achieved between the change in fair value of the hedge instrument and the cumulative change in expected future cash flows on the hedged transaction from inception of the hedge in a cash flow hedge or the change in the fair value. Ineffectiveness was insignificant for the years ended December 31, 2013, 2012 and 2011. See Note 11, "Derivatives" for further disclosures related to the Company's derivative instruments.
Fair Value	'
	Fair Value
	Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly hypothetical transaction between market participants at a given measurement date. Valuation techniques used must maximize the use of observable inputs and minimize the use of unobservable inputs. See Note 16, "Fair Values Measurements" for further disclosures related to the Company's recurring fair value estimates.
Income Taxes	'
	Income Taxes
	Deferred income taxes are provided for temporary differences arising from differences between the financial statement amount and tax basis of assets and liabilities existing at each balance sheet date using enacted tax rates anticipated to be in effect when the related taxes are expected to be paid or recovered. A valuation allowance is established if it is more likely than not that a deferred tax asset will not be realized. In determining the need for a valuation allowance, the Company considers projected realization of tax benefits based on expected levels of future taxable income, available tax planning strategies and the reversal of temporary differences.
	Benefits from tax positions that are uncertain are not recognized unless the Company concludes that it is more likely than not that the position would be sustained in a dispute with taxing authorities, should the dispute be taken to the court of last resort. The Company would measure any such benefit at the largest amount of benefit that is greater than 50 percent likely of being realized upon settlement with taxing authorities.
	See Note 14, "Taxes" for further disclosures about income taxes.
Benefit Plans	'
	Benefit Plans
	The Company has non-contributory defined benefit pension plans covering most of its salaried and hourly employees. Benefits are generally based on the employee's age and compensation. The Company also currently provides certain postretirement medical and life insurance coverage for eligible employees. The cost of providing these benefits are determined on an actuarial basis and accrued over the employee's period of active service.
	The Company recognizes the overfunded or underfunded status of these plans as determined on an actuarial basis on the balance sheet and the changes in the funded status are recognized in other comprehensive income. See Note 20, "Employee Benefit Plans" for additional disclosures relating to these obligations.
Stock-Based Compensation	'
	Stock-Based Compensation
	The compensation cost of all stock-based awards is determined based on the grant-date fair value of the award, and is recognized over the requisite service period. The grant-date fair value of option awards is determined using a Black-Scholes option pricing model. Compensation cost for an award with performance conditions is accrued if it is probable that the conditions will be met. See further discussion in Note 18, "Stock-Based Compensation and Other Incentive Plans."

Discontinued_Operations_Tables

Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2013
Discontinued Operations and Disposal Groups [Abstract]	'
Schedule of Disposal Groups, Including Discontinued Operations, Income Statement, Balance Sheet and Additional Disclosures [Table Text Block]	'
	Discontinued Operations
	As part of a strategy to divest its non-core thermal coal assets, the Company entered into a definitive agreement on June 27, 2013 to sell Canyon Fuel, to Bowie Resources, LLC. Canyon Fuel operated two longwall mining complexes and a continuous miner operation in Utah. The sale was completed on August 16, 2013, for $422.7 million in cash, including adjustments to working capital estimates.
	The following table summarizes the results of discontinued operations through the date of disposition:
			Year Ended December 31,
			2013		2012		2011
		(In thousands)
	Total Revenues		$	219,002	$	390,912	$	402,856
	Income from discontinued operations before income taxes		$	32,167	$	75,418	$	70,515
	Gain on sale		120,321		—		—
	Less: income tax expense		49,092		20,190		16,690
	Income from discontinued operations, including gain on sale - net of tax		$	103,396	$	55,228	$	53,825
	Basic earnings per common share from discontinued operations		$	0.49	$	0.26	$	0.28
	Diluted earnings per common share from discontinued operations		$	0.49	$	0.26	$	0.28
	The following table summarizes the assets and liabilities of the discontinued operations reflected in the December 31, 2012 consolidated balance sheet:
	Inventories	53,543
	Other current assets	10,763
	Net property, plant & equipment	280,109
	Other noncurrent assets	5,334
	Accounts payable and accrued expenses	27,419
	Other noncurrent liabilities	9,892
	The following table summarizes the results of discontinued operations through the date of disposition:
			Year Ended December 31,
			2013		2012		2011
		(In thousands)
	Total Revenues		$	219,002	$	390,912	$	402,856
	Income from discontinued operations before income taxes		$	32,167	$	75,418	$	70,515
	Gain on sale		120,321		—		—
	Less: income tax expense		49,092		20,190		16,690
	Income from discontinued operations, including gain on sale - net of tax		$	103,396	$	55,228	$	53,825
	Basic earnings per common share from discontinued operations		$	0.49	$	0.26	$	0.28
	Diluted earnings per common share from discontinued operations		$	0.49	$	0.26	$	0.28

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Abstract]	'
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	'
	The following items are included in accumulated other comprehensive income (loss):
							Pension,
							Postretirement
							and Other						Accumulated
							Post-						Other
			Derivative				Employment			Available-			Comprehensive
			Instruments				Benefits			for-Sale Securities			Income (Loss)
			(In thousands)
	Balance at	1-Jan-11	$	(4,729	)		$	(4,676	)	$	1,455		$	(7,950	)
	Unrealized gains (losses)		4,320				(14,528		)	(1,924		)	(12,132		)
	Amounts reclassified from accumulated other comprehensive income (loss)		2,653				918			4			3,575
	Balance at	31-Dec-12	2,244				(18,286		)	(465		)	(16,507		)
	Unrealized gains		168				48,482			5,935			54,585
	Amounts reclassified from accumulated other comprehensive income (loss)		(1,847		)		916			545			(386		)
	Balance at	31-Dec-13	$	565			$	31,112		$	6,015		$	37,692
Schedule of comprehensive income reclassifications [Table Text Block]	'
	The following amounts were reclassified out of accumulated other comprehensive income (loss) during the year ended December 31, 2013:
	Details about accumulated other			Reclassifications				Line Item in the Consolidated
	comprehensive income components			(in thousands)				Statement of Operations
	Derivative instruments			$	2,886			Revenues
				(1,039		)		Benefit from income taxes
				$	1,847			Net of tax
	Pension, postretirement and other post-employment benefits
	Amortization of prior service credits			$	13,705		1
	Amortization of actuarial gains (losses), net			(15,136		)	1
				(1,431		)		Total before tax
				515				Benefit from income taxes
				$	(916	)		Net of tax
	Available-for-sale securities			$	(852	)	2	Interest and investment income
				307				Benefit from income taxes
				$	(545	)		Net of tax
	1 Production-related benefits and workers' compensation costs are included in costs to produce coal. See Note 19, "Workers' Compensation Expense" and Note 20 "Employee Benefit Plans" for more information about pension, postretirement and postemployment benefit costs.
	2 The gains and losses on sales of available-for-sale-securities are determined on a specific identification basis.

Impairment_Charges_and_Mine_Cl1

Impairment Charges and Mine Closure Costs (Tables)	12 Months Ended
	Dec. 31, 2013
Impairment Charges and Mine Closure Costs [Abstract]	'
Restructuring and Related Costs [Table Text Block]	'
	In 2012, the closure and idling of mines in Appalachia discussed in Note 1, "Basis of Presentation" resulted in closure costs and related impairment charges that are reflected on the line "Asset impairment and mine closures costs" in the consolidated statements of operations.
		In millions
	Parts and supplies inventory writedown	$	2.6
	Impairment of property, plant and equipment	95.6
	Impairment of coal properties and deferred development costs	403.3
	Royalty obligations	11.5
	Employee termination benefits	12.3
	Pension, postretirement and occupational disease curtailment gain, net	(1.8		)
		$	523.5

Goodwill_Tables

Goodwill (Tables)	12 Months Ended
	Dec. 31, 2013
Goodwill and Intangible Assets Disclosure [Abstract]	'
Schedule of Goodwill [Table Text Block]	'
	Changes in the carrying value of goodwill for the three years ended December 31, 2013 are as follows:
		(In thousands)
	Balance at January 1, 2011	$	114,963
	Consideration paid related to prior business acquisitions	829
	Acquisition of ICG	480,311
	Balance at December 31, 2011	596,103
	Impairment	(330,680		)
	Balance at December 31, 2012	265,423
	Impairment	(265,423		)
	Balance at December 31, 2013	$	—

Inventories_Tables

Inventories (Tables)	12 Months Ended
	Dec. 31, 2013
Inventory Disclosure [Abstract]	'
Inventories	'
	Inventories consist of the following:
		31-Dec
		2013		2012
		(In thousands)
	Coal	$	117,531	$	180,917
	Repair parts and supplies	137,497		172,139
	Work-in-process	9,133		12,368
		$	264,161	$	365,424

Investments_in_AvailableforSal1

Investments in Available-for-Sale Securities (Tables)	12 Months Ended
	Dec. 31, 2013
Available-for-sale Securities [Abstract]	'
Available-for-sale Securities [Table Text Block]	'
	The Company's investments in available-for-sale marketable securities are as follows:
		December 31, 2013
											Balance Sheet
				Gross		Gross					Classification
				Unrealized		Unrealized			Fair		Short-Term		Other
		Cost Basis		Gains		Losses			Value		Investments		Assets
		(In thousands)
	Available-for-sale:
	U.S. government and agency securities	$	65,002	$	12	$	(75	)	$	64,938	$	64,938	$	—
	Corporate notes and bonds	184,773		6		(1,304		)	183,476		183,476		—
	Equity securities	5,271		13,660		(2,902		)	16,029		—		16,029
	Total Investments	$	255,046	$	13,678	$	(4,281	)	$	264,443	$	248,414	$	16,029
		December 31, 2012
											Balance Sheet
				Gross		Gross					Classification
				Unrealized		Unrealized			Fair		Short-Term		Other
		Cost Basis		Gains		Losses			Value		Investments		Assets
		(In thousands)
	Available-for-sale:
	U.S. government and agency securities	$	146,993	$	2	$	(412	)	$	146,583	$	146,583	$	—
	Corporate notes and bonds	88,118		—		(396		)	87,722		87,722		—
	Equity securities	5,271		2,704		(2,628		)	5,347		—		5,347
	Total Investments	$	240,382	$	2,706	$	(3,436	)	$	239,652	$	234,305	$	5,347

Equity_Investments_and_Members1

Equity Investments and Membership Interests in Joint Ventures (Tables)	12 Months Ended
	Dec. 31, 2013
Equity Method Investments and Joint Ventures [Abstract]	'
Schedule Of Equity Method Investments	'
	Below are the equity method investments reflected in the consolidated balance sheets:
	Investee	Knight Hawk			DKRW			DTA			Tenaska			Millennium			Tongue River			Other		Total
	Balance at December 31, 2010	$	131,250		$	21,961		$	14,472		$	9,768		$	—		$	—		$	—	$	177,451
	Investments in affiliates	—			—			—			5,500			25,000			12,989			—		43,489
	Advances to (distributions from) affiliates, net	(16,621		)	—			6,498			—			3,477			—			—		(6,646		)
	Equity in comprehensive income (loss)	20,596			(2,246		)	(4,884		)	(2		)	(2,153		)	—			—		11,311
	Balance at December 31, 2011	135,225			19,715			16,086			15,266			26,324			12,989			—		225,605
	Investments in affiliates	—			—			—			—			—			—			—		—
	Advances to (distributions from) affiliates, net	(7,151		)	—			4,335			—			8,798			1,708			—		7,690
	Equity in comprehensive income (loss)	20,989			(4,200		)	(4,959		)	(2		)	(2,908		)	—			—		8,920
	Balance at December 31, 2012	149,063			15,515			15,462			15,264			32,214			14,697			—		242,215
	Advances to (distributions from) affiliates, net	(13,536		)	—			3,644			—			6,476			4,004			200		788
	Equity in comprehensive income (loss)	17,279			(1,832		)	(4,969		)	—			(2,796		)	(282		)	—		7,400
	Impairment of equity investment	—			(13,683		)	—			(15,264		)	—			—			—		(28,947		)
	Balance at December 31, 2013	$	152,806		$	—		$	14,137		$	—		$	35,894		$	18,419		$	200	$	221,456

Acquired_Sales_Contracts_Table

Acquired Sales Contracts (Tables)	12 Months Ended
	Dec. 31, 2013
Acquired Sales Contracts [Abstract]	'
Schedule Of Acquired Sales Contracts [Table Text Block]	'
	The acquired sales contracts reflected in the consolidated balance sheets are as follows:
		December 31, 2013						December 31, 2012
		Assets			Liabilities			Assets			Liabilities
		(In thousands)						(In thousands)
	Acquired fair value	$	131,819		$	166,697		$	131,819		$	166,697
	Accumulated amortization	(129,449		)	(120,367		)	(123,776		)	(105,237		)
	Total	$	2,370		$	46,330		$	8,043		$	61,460
	Net total				$	(43,960	)				$	(53,417	)
	Balance Sheet classification:
	Other current	$	1,324		$	14,373		$	5,651		$	14,038
	Other noncurrent	$	1,046		$	31,957		$	2,392		$	47,422

Derivatives_Tables

Derivatives (Tables)	12 Months Ended
	Dec. 31, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Schedule of Price Risk Derivatives	'
	At December 31, 2013, the Company held derivatives for risk management purposes that are expected to settle in the following years:
	(Tons in thousands)		2014			2015			Total
	Coal sales		4,845			900			5,745
	Coal purchases		1,561			—			1,561
Disclosure Of Fair Value Of Derivatives	'
			31-Dec-13											31-Dec-12
	Fair Value of Derivatives		Asset				Liability							Asset				Liability
	(In thousands)		Derivative				Derivative							Derivative				Derivative
	Derivatives Designated as Hedging Instruments
	Coal		$	909			$	(26	)					$	3,277			$	(10	)
	Derivatives Not Designated as Hedging Instruments
	Heating oil -- diesel purchases		4,681				—							7,379				—
	Heating oil -- fuel surcharges		422				—							1,961				—
	Coal -- held for trading purposes		55,327				(45,763		)					17,403				(16,933		)
	Coal -- risk management		6,342				(1,950		)					24,843				(7,342		)
	Total		66,772				(47,713		)					51,586				(24,275		)
	Total derivatives		67,681				(47,739		)					54,863				(24,285		)
	Effect of counterparty netting		(47,727		)		47,727							(22,548		)		22,548
	Net derivatives as classified in the balance sheets		$	19,954			$	(12	)		$	19,942		$	32,315			$	(1,737	)		$	30,578
					31-Dec-13				31-Dec-12
	Net derivatives as reflected on the balance sheets
	Heating oil		Other current assets		$	5,103			$	9,340
	Coal		Coal derivative assets		14,851				22,975
			Coal derivative liabilities		(12		)		(1,737		)
					$	19,942			$	30,578
Effects Of Derivatives On Measures Of Financial Performance	'
	Derivatives used in Cash Flow Hedging Relationships (in thousands)
	For the year ended December 31
			Gain (Loss) Recognized in Other Comprehensive Income(Effective Portion)													Gains (Losses) Reclassified from Other Comprehensive Income into Income
																(Effective Portion)
			2013				2012				2011					2013				2012				2011
	Coal sales	(1)	$	(338	)		$	7,690			4,923					$	3,664			$	2,675			$	1,572
	Coal purchases	(2)	526				(2,440		)		(2,009		)			(683		)		—				—
			$	188			$	5,250			$	2,914				$	2,981			$	2,675			$	1,572
	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 year ended December 31, 2013 and 2012.
	Derivatives Not Designated as Hedging Instruments (in thousands)
	For the year ended December 31
			Gain (Loss) Recognized
			2013				2012				2011
	Coal — unrealized	(3)	$	(12,700	)		$	8,272			$	6,438
	Coal — realized	(4)	$	32,534			$	43,990			$	(7	)
	Heating oil — diesel purchases	(4)	$	(9,791	)		$	(22,281	)		$	(2,906	)
	Heating oil — fuel surcharges	(4)	$	(947	)		$	(2,209	)		$	—
	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, net
	During the first quarter of 2012, the Company determined that the effectiveness of heating oil options as a hedge for diesel fuel purchases could not be established as of December 31, 2011. As a result, the amount remaining in accumulated other comprehensive income of $8.2 million was recorded in the "Other operating income, net" line in the consolidated statement of operations, or $5.2 million, net of income taxes. In 2011, unrealized gains of $1.3 million were recognized in other comprehensive income and gains of $14.9 million were reclassified from other comprehensive income into earnings relating to heating oil positions.
	The effects of derivatives on measures of financial performance are as follows:
	Derivatives used in Cash Flow Hedging Relationships (in thousands)
	For the year ended December 31
			Gain (Loss) Recognized in Other Comprehensive Income(Effective Portion)													Gains (Losses) Reclassified from Other Comprehensive Income into Income
																(Effective Portion)
			2013				2012				2011					2013				2012				2011
	Coal sales	(1)	$	(338	)		$	7,690			4,923					$	3,664			$	2,675			$	1,572
	Coal purchases	(2)	526				(2,440		)		(2,009		)			(683		)		—				—
			$	188			$	5,250			$	2,914				$	2,981			$	2,675			$	1,572
	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 year ended December 31, 2013 and 2012.
	Derivatives Not Designated as Hedging Instruments (in thousands)
	For the year ended December 31
			Gain (Loss) Recognized
			2013				2012				2011
	Coal — unrealized	(3)	$	(12,700	)		$	8,272			$	6,438
	Coal — realized	(4)	$	32,534			$	43,990			$	(7	)
	Heating oil — diesel purchases	(4)	$	(9,791	)		$	(22,281	)		$	(2,906	)
	Heating oil — fuel surcharges	(4)	$	(947	)		$	(2,209	)		$	—
	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, net

Accrued_Expenses_and_Other_Cur1

Accrued Expenses and Other Current Liabilities Accrued Expenses and Other Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2013
Accrued Expenses and Other Current Liabilities [Abstract]	'
Schedule of Accrued Liabilities [Table Text Block]	'
	Accrued expenses and other current liabilities consist of the following:
		December 31,
		2013		2012
		(In thousands)
	Payroll and employee benefits	$	67,621	$	72,405
	Taxes other than income taxes	114,664		121,029
	Interest	18,528		42,413
	Acquired sales contracts	14,373		14,038
	Workers’ compensation	12,434		10,371
	Asset retirement obligations	24,940		38,920
	Other	26,015		18,842
		$	278,575	$	318,018

Debt_and_Financing_Arrangement1

Debt and Financing Arrangements (Tables)	12 Months Ended
	Dec. 31, 2013
Debt Disclosure [Abstract]	'
Debt	'
		December 31,
		2013		2012
		(In thousands)
	Term loan due 2018 ($1.93 billion and $1.65 billion face value, respectively)	$	1,906,975	$	1,627,384
	8.75% senior notes ($600.0 million face value) due 2016	—		590,999
	7.00% senior notes due 2019 at par	1,000,000		1,000,000
	8.00% senior secured notes due 2019 at par	350,000		—
	9.875% senior notes ($375.0 million face value) due 2019	362,358		360,042
	7.25% senior notes due 2020 at par	500,000		500,000
	7.25% senior notes due 2021 at par	1,000,000		1,000,000
	Other	32,162		40,350
		5,151,495		5,118,775
	Less current maturities of debt	33,493		32,896
	Long-term debt	$	5,118,002	$	5,085,879

Taxes_Tables

Taxes (Tables)	12 Months Ended
	Dec. 31, 2013
Taxes [Abstract]	'
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	'
	Significant components of the provision for (benefit from) income taxes are as follows:
		Year Ended December 31
		2013			2012			2011
		(In thousands)
	Current:
	Federal	$	—		$	(20,022	)	$	(24,449	)
	State	(647		)	575			1,072
	Total current	(647		)	(19,447		)	(23,377		)
	Deferred:
	Federal	(318,956		)	(341,486		)	1,544
	State	(15,895		)	7,026			(2,446		)
	Total deferred	(334,851		)	(334,460		)	(902		)
		$	(335,498	)	$	(353,907	)	$	(24,279	)
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	'
	A reconciliation of the statutory federal income tax provision (benefit) at the statutory rate to the actual provision for (benefit from) income taxes follows:
		Year Ended December 31
		2013			2012			2011
		(In thousands)
	Income tax provision (benefit) at statutory rate	$	(378,463	)	$	(382,581	)	$	22,253
	Percentage depletion allowance	(15,796		)	(33,654		)	(53,156		)
	Goodwill	70,301			56,916			—
	State taxes, net of effect of federal taxes	(25,265		)	(24,231		)	(3,790		)
	Change in valuation allowance	8,659			31,832			2,416
	Other, net	5,066			(2,189		)	7,998
		$	(335,498	)	$	(353,907	)	$	(24,279	)
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	'
	Significant components of the Company's deferred tax assets and liabilities that result from carryforwards and temporary differences between the financial statement basis and tax basis of assets and liabilities are summarized as follows:
		December 31,
		2013			2012
		(In thousands)
	Deferred tax assets:
	Net operating loss carryforwards	$	660,916		$	496,330
	Alternative minimum tax credit carryforwards	126,755			150,014
	Reclamation and mine closure	113,843			104,570
	Goodwill	52,636			43,839
	Acquired sales contracts	33,392			38,735
	Workers' compensation	31,641			32,241
	Retiree benefit plans	20,527			32,087
	Share based compensation	28,494			25,440
	Contract obligations	19,327			21,798
	Other, primarily accrued liabilities	68,969			66,777
	Gross deferred tax assets	1,156,500			1,011,831
	Valuation allowance	(43,322		)	(34,663		)
	Total deferred tax assets	1,113,178			977,168
	Deferred tax liabilities:
	Plant and equipment	1,364,382			1,411,446
	Deferred development	91,126			77,013
	Investment in tax partnerships	8,170			72,513
	Other	13,902			13,018
	Total deferred tax liabilities	1,477,580			1,573,990
	Net deferred liability	$	364,402		$	596,822
	Current asset	$	49,144		$	67,360
	Non-current deferred tax liability	$	413,546		$	664,182
Summary of Income Tax Contingencies [Table Text Block]	'
	A reconciliation of the beginning and ending amounts of gross unrecognized tax benefits follows:
		(In thousands)
	Balance at January 1, 2011	$	4,418
	Additions based on tax positions related to the current year	1,626
	Additions for tax positions of prior years	2,754
	Balance at December 31, 2011	8,798
	Additions based on tax positions related to the current year	409
	Additions for tax positions of prior years	21,943
	Balance at December 31, 2012	31,150
	Additions based on tax positions related to the current year	1,199
	Additions for tax positions of prior years	688
	Reductions as a result of lapses in the statute of limitations	(1,248		)
	Balance at December 31, 2013	$	31,789

Asset_Retirement_Obligations_T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2013
Asset Retirement Obligation [Abstract]	'
Schedule of Change in Asset Retirement Obligation [Table Text Block]	'
	The following table describes the changes to the Company's asset retirement obligation liability:
		Year Ended December 31,
		2013			2012
		(In thousands)
	Balance at January 1 (including current portion)	$	448,625		$	473,903
	Accretion expense	35,727			39,020
	Obligations of divested operations	(8,440		)	—
	Adjustments to the liability from changes in estimates	(26,578		)	4,400
	Liabilities settled	(21,681		)	(68,698		)
	Balance at December 31	$	427,653		$	448,625
	Current portion included in accrued expenses	(24,940		)	(38,920		)
	Noncurrent liability	$	402,713		$	409,705

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2013
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 consolidated balance sheet:
		Fair Value at							31-Dec-13
		Total				Level 1				Level 2			Level 3
		(In thousands)
	Assets:
	Investments in marketable securities	$	264,443			$	77,967			$	186,476		$	—
	Derivatives	19,954				14,847				—			5,107
	Total assets	$	284,397			$	92,814			$	186,476		$	5,107
	Liabilities:
	Derivatives	$	12			$	—			$	(149	)	$	161
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.
			Year Ended December 31,
			2013				2012
			(In thousands)
	Balance, beginning of period		$	8,174			$	6,211
	Realized and unrealized losses recognized in earnings, net		(10,253		)		(13,399		)
	Purchases		8,654				—
	Issuances		(25		)		17,312
	Settlements		(1,604		)		(1,950		)
	Ending balance		$	4,946			$	8,174

StockBased_Compensation_and_Ot1

Stock-Based Compensation and Other Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2013
Share-based Compensation [Abstract]	'
Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block]	'
	Information regarding stock option activity under the Incentive Plan follows for the year ended December 31, 2013:
					Weighted Average			Aggregate				Average
		Common			Exercise			Intrinsic				Contract
		Shares			Price			Value				Life
		(In thousands)
	Options outstanding at January 1	5,215			$	25.89
	Granted	1,998			5.23
	Canceled	(138	)		29.01
	Expired	(136	)		31.57
	Options outstanding at December 31	6,939			19.86			$	3			6.7
	Options exercisable at December 31	3,724			28.14			—				5.3
Schedule of Nonvested Share Activity [Table Text Block]	'
	Information regarding changes in stock options outstanding and not yet vested and the related grant-date fair value under the Incentive Plan follows for the year ended December 31, 2013:
				Weighted Average
		Common Shares		Grant-Date Fair Value
		(In thousands)
	Unvested options at January 1	2,369		$	7.72
	Granted	1,998		$	2.37
	Vested	-1,098		$	8.11
	Canceled	-53		$	3.97
	Unvested options at December 31	3,216		$	4.38
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]	'
	Weighted average assumptions used in the Black-Scholes option pricing model for granted options follow:
		Year Ended December 31,
		2013				2012			2011
	Weighted average grant-date fair value per share of options granted	$	2.37			$	5.27		$	14.18
	Assumptions (weighted average):
	Risk-free interest rate	0.65%				0.76%			1.92%
	Expected dividend yield	2.30%				2.92%			1.25%
	Expected volatility	66.70%				60.70%			57.40%
	Expected life (in years)	4.5				4.5			4.5
Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]	'
	Information regarding restricted stock and restricted stock unit activity and weighted average grant-date fair value follows for the year ended December 31, 2013:
		Restricted Stock						Restricted Stock Units
					Weighted Average						Weighted Average
		Common			Grant-Date			Common			Grant-Date
		Shares			Fair Value			Shares			Fair Value
		(In thousands)						(In thousands)
	Outstanding at January 1	188			$	25.14		511			$	13.26
	Granted	—						969			5.2
	Vested	(44	)		17.3			(39	)		9.19
	Canceled	—			—			(19	)		7.21
	Outstanding at December 31	144			27.55			1,422			7.96

Workers_Compensation_Expense_T

Workers' Compensation Expense (Tables)	12 Months Ended
	Dec. 31, 2013
Workers' Compensation Expense [Abstract]	'
Workers' Compensation Expense	'
			Year Ended December 31,
			2013		2012		2011
		(In thousands)
	Total occupational disease		6,137		6,962		3,365
	Traumatic injury claims and assessments		21,089		26,565		16,979
	Total workers’ compensation expense		$	27,226	$	33,527	$	20,344

Employee_Benefit_Plans_Tables

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2013
Pension and Other Postretirement Benefit Expense [Abstract]	'
Pension Benefit Costs	'
	Summaries of the changes in the benefit obligations, plan assets and funded status of the plans are as follows:
										Other Postretirement
		Pension Benefits								Benefits
		2013				2012				2013				2012
		(In thousands)
	CHANGE IN BENEFIT OBLIGATIONS
	Benefit obligations at January 1	$	390,894			$	333,951			$	49,326			$	45,129
	Service cost	27,065				27,466				2,027				2,142
	Interest cost	16,207				15,668				1,739				2,020
	Plan amendments	—				—				—				2,183
	Benefits paid	(41,562		)		(23,624		)		(3,276		)		(4,244		)
	Curtailments	(3,027		)		(687		)		(2,519		)		(708		)
	Other-primarily actuarial loss (gain)	(34,109		)		38,120				(4,766		)		2,804
	Benefit obligations at December 31	$	355,468			$	390,894			$	42,531			$	49,326
	CHANGE IN PLAN ASSETS
	Value of plan assets at January 1	$	322,874			$	285,074			$	—			$	—
	Actual return on plan assets	52,247				42,396				—				—
	Employer contributions	14,393				19,028				3,276				4,244
	Benefits paid	(41,562		)		(23,624		)		(3,276		)		(4,244		)
	Value of plan assets at December 31	$	347,952			$	322,874			$	—			$	—
	Accrued benefit cost	$	(7,516	)		$	(68,020	)		$	(42,531	)		$	(49,326	)
	ITEMS NOT YET RECOGNIZED AS A COMPONENT OF NET PERIODIC BENEFIT COST
	Prior service credit (cost)	$	1,732			$	1,890			$	31,925			$	45,938
	Accumulated gain (loss)	10,096				(68,915		)		3,394				(1,531		)
		$	11,828			$	(67,025	)		$	35,319			$	44,407
	BALANCE SHEET AMOUNTS
	Current liability	$	(405	)		$	(390	)		$	(3,276	)		$	(4,240	)
	Noncurrent liability	$	(7,111	)		$	(67,630	)		$	(39,255	)		$	(45,086	)
		$	(7,516	)		$	(68,020	)		$	(42,531	)		$	(49,326	)
Other Postretirement Benefit Costs Table Text Block [Table Text Block]	'
														Other Postretirement
		Pension Benefits												Benefits
		Year Ended December 31,												Year Ended December 31,
		2013				2012				2011				2013				2012			2011
		(In thousands)
	Service cost	$	27,065			$	27,466			$	16,490			$	2,027			$	2,142		$	3,917
	Interest cost	16,207				15,668				16,253				1,739				2,020			3,279
	Curtailments	47				324				—				(5,444		)		(4,049		)	—
	Expected return on plan assets	(23,761		)		(22,030		)		(21,812		)		—				—			—
	Amortization of prior service credits	(204		)		259				(189		)		(10,621		)		(11,458		)	(2,364		)
	Amortization of other actuarial losses (gains)	14,616				14,666				8,748				(252		)		(522		)	(3,100		)
	Net benefit cost (credit)	$	33,970			$	36,353			$	19,490			$	(12,551	)		$	(11,867	)	$	1,732
Schedule of Assumptions Used [Table Text Block]	'
	Assumptions. The following table provides the assumptions used to determine the actuarial present value of projected benefit obligations at December 31.
		Pension Benefits				Other Postretirement Benefits
		2013		2012		2013		2012
	Weighted average assumptions:
	Discount rate	5.08%		4.13%		4.58%		3.64%
	Rate of compensation increase	3.39%		3.39%		N/A		N/A
	The following table provides the assumptions used to determine net periodic benefit cost for years ended December 31.
		Pension Benefits									Other Postretirement Benefits
		2013					2012		2011		2013				2012		2011
	Weighted average assumptions:
	Discount rate	4.13	%	/	5.05%		4.91%		5.71%		3.64%	/	4.58%		4.52%		5.23%
	Rate of compensation increase	3.39%					3.39%		3.39%		N/A				N/A		N/A
	Expected return on plan assets	7.75%					7.75%		8.50%		N/A				N/A		N/A
Schedule of Allocation of Plan Assets [Table Text Block]	'
	The Company's pension plan assets at December 31, 2013 and 2012, respectively, are categorized below according to the fair value hierarchy as defined in Note 16, "Fair Value Measurements":
		Total								Level 1								Level 2						Level 3
		2013				2012				2013				2012				2013			2012			2013		2012
		(In thousands)
	Equity Securities:(A)
	U.S. small-cap	$	14,901			$	13,099			$	14,901			$	13,099			$	—		$	—		$	—	$	—
	U.S. mid-cap	62,271				43,946				28,654				12,717				33,617			31,229			—		—
	U.S. large-cap	110,947				102,922				53,708				48,536				57,239			54,386			—		—
	Non-U.S.	29,165				27,251				—				—				29,165			27,251			—		—
	Fixed income securities:
	U.S. government securities(B)	18,545				24,202				17,714				23,483				831			719			—		—
	Non-U.S. government securities(C)	2,143				3,681				—				—				2,143			3,681			—		—
	U.S. government asset and mortgage backed securities(D)	600				781				—				—				600			781			—		—
	Corporate fixed income(E)	9,902				14,016				—				—				9,902			14,016			—		—
	State and local government securities(F)	8,301				9,903				—				—				8,301			9,903			—		—
	Other fixed income(G)	58,093				61,765				—				—				58,093			61,765			—		—
	Short-term investments(H)	14,663				20,894				—				—				14,663			20,894			—		—
	Other investments(I)	18,421				414				—				—				1,404			414			17,017		—
	Total	$	347,952			$	322,874			$	114,977			$	97,835			$	215,958		$	225,039		$	17,017	$	—
	(A) Equity securities includes investments in 1) common stock, 2) preferred stock and 3) mutual funds. Investments in common and preferred stocks are valued using quoted market prices multiplied by the number of shares owned. Investments in mutual funds are valued at the net asset value per share multiplied by the number of shares held as of the measurement date and are traded on listed exchanges.
	(B) U.S. government securities includes agency and treasury debt. These investments are valued using dealer quotes in an active market.
	(C) Non-U.S. government securities includes debt securities issued by foreign governments and are valued utilizing a price spread basis valuation technique with observable sources from investment dealers and research vendors.
	(D) U.S. government asset and mortgage backed securities includes government-backed mortgage funds which are valued utilizing an income approach that includes various valuation techniques and sources such as discounted cash flows models, benchmark yields and securities, reported trades, issuer trades and/or other applicable data.
	(E) Corporate fixed income is primarily comprised of corporate bonds and certain corporate asset-backed securities that are denominated in the U.S. dollar and are investment-grade securities. These investments are valued using dealer quotes.
	(F) State and local government securities include different U.S. state and local municipal bonds and asset backed securities, these investments are valued utilizing a market approach that includes various valuation techniques and sources such as value generation models, broker quotes, benchmark yields and securities, reported trades, issuer trades and/or other applicable data.
	(G) Other fixed income investments are actively managed fixed income vehicles that are valued at the net asset value per share multiplied by the number of shares held as of the measurement date.
	(H) Short-term investments include governmental agency funds, government repurchase agreements, commingled funds, and pooled funds and mutual funds. Governmental agency funds are valued utilizing an option adjusted spread valuation technique and sources such as interest rate generation processes, benchmark yields and broker quotes. Investments in governmental repurchase agreements, commingled funds and pooled funds and mutual funds are valued at the net asset value per share multiplied by the number of shares held as of the measurement date.
	(I) Other investments includes cash, forward contracts, derivative instruments, credit default swaps, interest rate swaps and mutual funds. Investments in interest rate swaps are valued utilizing a market approach that includes various valuation techniques and sources such as value generation models, broker quotes in active and non-active markets, benchmark yields and securities, reported trades, issuer trades and/or other applicable data. Forward contracts and derivative instruments are valued at their exchange listed price or broker quote in an active market. The mutual funds are valued at the net asset value per share multiplied by the number of shares held as of the measurement date and are traded on listed exchanges.
Schedule of Expected Benefit Payments [Table Text Block]	'
	The following represents expected future benefit payments from the plan, which reflect expected future service, as appropriate:
						Other
		Pension				Postretirement
		Benefits				Benefits
		(In thousands)
	2014	$	21,844			$	4,020
	2015	21,666				4,226
	2016	27,689				4,415
	2017	29,999				4,523
	2018	33,488				4,602
	Years 2019-2023	190,030				22,028
		$	324,716			$	43,814

Leases_Tables

Leases (Tables)	12 Months Ended
	Dec. 31, 2013
Leases [Abstract]	'
Operating Leases of Lessee Disclosure [Table Text Block]	'
	Minimum payments due in future years under these agreements in effect at December 31, 2013 are as follows:
		Operating
		Leases		Royalties
		(In thousands)
	2014	$	31,532	$	17,394
	2015	24,466		19,143
	2016	16,851		21,070
	2017	14,509		20,806
	2018	3,739		22,255
	Thereafter	1,195		83,708
		$	92,292	$	184,376

Risk_Concentrations_Tables

Risk Concentrations (Tables)	12 Months Ended
	Dec. 31, 2013
Risks Concentrations [Abstract]	'
Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block]	'
	The Company uses shipping destination as the basis for attributing revenue to individual countries. The Company's foreign revenues by geographical location are as follows:
		Year Ended December 31, 2013
		(In thousands)
	Europe (includes Morocco)	$	371,363
	Asia	160,404
	North America	80,322
	Central and South America	55,493
	Brokered Sales	154,442
	Total	$	822,024

Segment_Information_Tables

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2013
Segment Reporting [Abstract]	'
Schedule Of Operating Segment Results	'
			PRB			APP				Other			Corporate,			Consolidated
										Operating			Other and
										Segments			Eliminations
			(in thousands)
	Year Ended December 31,	2013
	Revenues		$	1,482,813		$	1,145,800			$	385,744		$	—		$	3,014,357
	Income (loss) from operations		41,543			(108,387		)		64,943			(661,240		)	(663,141		)
	Depreciation, depletion and amortization		171,324			202,952				45,741			6,425			426,442
	Amortization of acquired sales contracts, net		(3,656		)	(10,364		)		4,563			—			(9,457		)
	Total assets		1,841,835			3,971,764				402,922			2,773,672			8,990,193
	Capital expenditures		9,784			167,759				23,122			96,319			296,984
	Year Ended December 31,	2012
	Revenues		$	1,524,536		$	1,793,576			$	450,014		$	—		$	3,768,126
	Income (loss) from operations		100,679			(606,235		)		74,142			(325,598		)	(757,012		)
	Depreciation, depletion and amortization		166,539			271,220				49,911			4,541			492,211
	Amortization of acquired sales contracts, net		(1,987		)	(23,926		)		724			—			(25,189		)
	Total assets		1,972,522			3,875,105				834,287			3,324,863			10,006,777
	Capital expenditures		23,410			275,476				68,220			28,119			395,225
	Year Ended December 31,	2011
	Revenues		$	1,646,947		$	1,915,090			$	321,002		$	—		$	3,883,039
	Income (loss) from operations		180,730			283,404				44,465			(165,538		)	343,061
	Depreciation, depletion and amortization		171,693			203,759				43,504			2,024			420,980
	Amortization of acquired sales contracts, net		19,458			(39,988		)		(1,539		)	—			(22,069		)
	Total assets		2,307,783			4,740,723				1,262,433			1,903,020			10,213,959
	Capital expenditures		110,999			217,435				94,599			117,903			540,936
Reconciliation Statement Of Segment Income From Operations To Consolidated Income Before Income Taxes	'
	A reconciliation of segment income (loss) from operations to consolidated loss before income taxes follows:
			Year Ended December 31,
			2013			2012			2011
	Loss from operations		$	(663,141	)	$	(757,012	)	$	343,061
	Interest expense		(381,267		)	(317,615		)	(230,186		)
	Interest and investment income		6,603			5,473			3,309
	Nonoperating expense		(42,921		)	(23,668		)	(51,448		)
	Loss from continuing operations before income taxes		$	(1,080,726	)	$	(1,092,822	)	$	64,736

Quarterly_Financial_Informatio1

Quarterly Financial Information (Tables)	12 Months Ended
	Dec. 31, 2013
Quarterly Financial Information [Abstract]	'
Schedule of Quarterly Financial Information [Table Text Block]	'
	Quarterly selected financial data for the years ended December 31, 2013 and 2012 is summarized below:
		31-Mar			30-Jun			30-Sep			31-Dec
		(b)			(a)			(a) (b)			(a) (b)
		(In thousands, except per share data)
	2013:00:00
	Revenues	$	737,370		$	766,332		$	791,269		$	719,386
	Gross profit (loss)	$	(18,560	)	$	2,505		$	90		$	(44,801	)
	Asset impairment and mine closure costs	$	—		$	20,482		$	200,397		$	—
	Goodwill impairment	$	—		$	—		$	—		$	265,423
	Loss from operations	$	(51,431	)	$	(36,279	)	$	(234,753	)	$	(340,678	)
	Loss from continuing operations	$	(84,316	)	$	(80,351	)	$	(207,767	)	$	(372,794	)
	Income from discontinued operations, net of tax	$	14,267		$	8,145		$	79,404		$	1,580
	Net loss	$	(70,049	)	$	(72,206	)	$	(128,363	)	$	(371,214	)
	Diluted loss per common share
	Loss from continuing operations	$	(0.40	)	$	(0.38	)	$	(0.98	)	$	(1.76	)
	Net loss attributable to Arch Coal, Inc.	$	(0.33	)	$	(0.34	)	$	(0.61	)	$	(1.75	)
		31-Mar			30-Jun			30-Sep			31-Dec
		(b)			(a)			(a)			(a)
		(In thousands, except per share data)
	2012:00:00
	Revenues	$	960,237		$	965,685		$	975,170		$	867,034
	Gross profit	$	37,715		$	47,163		$	53,017		$	12,516
	Asset impairment and mine closure costs	$	—		$	525,583		$	(2,144	)	$	15,743
	Goodwill impairment	$	—		$	115,791		$	—		$	214,889
	Income (loss) from operations	$	27,797		$	(596,893	)	$	119,242		$	(307,158	)
	Income (loss) from continuing operations	$	(14,099	)	$	(442,456	)	$	24,673		$	(307,033	)
	Income from discontinued operations, net of tax	$	15,508		$	7,032		$	21,078		$	11,610
	Net income (loss)	$	1,409		$	(435,424	)	$	45,751		$	(295,423	)
	Diluted income (loss) per common share
	Income (loss) from continuing operations	$	(0.07	)	$	(2.09	)	$	0.12		$	(1.45	)
	Net loss attributable to Arch Coal, Inc.	$	0.01		$	(2.05	)	$	0.22		$	(1.39	)

Supplemental_Consolidating_Fin1

Supplemental Consolidating Financial Information (Tables)	12 Months Ended
	Dec. 31, 2013
Supplemental Condensed Consolidating Financial Information [Abstract]	'
Schedule of Condensed Consolidating Statements of Income [Table Text Block]	'
	Condensed Consolidating Statements of Operations and Comprehensive Income
	Year Ended December 31, 2013
		Parent/Issuer			Guarantor			Non-			Eliminations			Consolidated
					Subsidiaries			Guarantor
								Subsidiaries
		(In thousands)
	Revenues	$	—		$	3,014,357		$	—		$	—		$	3,014,357
	Costs, expenses and other
	Cost of sales (exclusive of items shown separately below)	9,117			2,657,583			—			(3,564		)	2,663,136
	Depreciation, depletion and amortization	5,949			420,458			35			—			426,442
	Amortization of acquired sales contracts, net	—			(9,457		)	—			—			(9,457		)
	Change in fair value of coal derivatives and coal trading activities, net	—			7,845			—			—			7,845
	Asset impairment and mine closure costs	78,150			142,729			—			—			220,879
	Goodwill impairment	—			265,423			—			—			265,423
	Selling, general and administrative expenses	88,820			39,825			7,038			(2,235		)	133,448
	Other operating income, net	4,209			(34,856		)	(5,370		)	5,799			(30,218		)
		186,245			3,489,550			1,703			—			3,677,498
	Loss from investment in subsidiaries	(328,889		)	—			—			328,889			—
	Loss from operations	(515,134		)	(475,193		)	(1,703		)	328,889			(663,141		)
	Interest expense, net
	Interest expense	(449,614		)	(24,747		)	(4,214		)	97,308			(381,267		)
	Interest and investment income	30,285			68,248			5,378			(97,308		)	6,603
		(419,329		)	43,501			1,164			—			(374,664		)
	Net loss resulting from early retirement and refinancing of debt	(42,921		)	—			—			—			(42,921		)
	Loss from continuing operations before income taxes	(977,384		)	(431,692		)	(539		)	328,889			(1,080,726		)
	Provision for (benefit from) income taxes	(335,552		)	—			54			—			(335,498		)
	Loss from continuing operations	(641,832		)	(431,692		)	(593		)	328,889			(745,228		)
	Income from discontinued operations, including gain on sale - net of tax	—			103,396			—			—			103,396
	Net loss	$	(641,832	)	$	(328,296	)	$	(593	)	$	328,889		$	(641,832	)
	Total comprehensive loss	$	(587,633	)	$	(304,278	)	$	(593	)	$	304,871		$	(587,633	)
	Condensed Consolidating Statements of Operations and Comprehensive Income
	Year Ended December 31, 2012
		Parent/Issuer			Guarantor			Non-			Eliminations			Consolidated
					Subsidiaries			Guarantor
								Subsidiaries
		(In thousands)
	Revenues	$	—		$	3,768,126		$	—		$	—		$	3,768,126
	Costs, expenses and other													—
	Cost of sales (exclusive of items shown separately below)	10,921			3,144,178			—			—			3,155,099
	Depreciation, depletion and amortization	5,392			486,786			33			—			492,211
	Amortization of acquired sales contracts, net	—			(25,189		)	—			—			(25,189		)
	Change in fair value of coal derivatives and coal trading activities, net	—			(16,590		)	—			—			(16,590		)
	Asset impairment and mine closure costs	—			539,182			—			—			539,182
	Goodwill impairment	—			330,680			—			—			330,680
	Contract settlement resulting from Patriot Coal bankruptcy	—			58,335			—			—			58,335
	Reduction in accrual related to acquired litigation	—			(79,532		)	—			—			(79,532		)
	Selling, general and administrative expenses	84,199			44,363			8,785			(3,048		)	134,299
	Other operating income, net	(13,392		)	(39,209		)	(13,804		)	3,048			(63,357		)
		87,120			4,443,004			(4,986		)	—			4,525,138
	Loss from investment in subsidiaries	(589,665		)	—			—			589,665			—
	Income (loss) from operations	(676,785		)	(674,878		)	4,986			589,665			(757,012		)
	Interest expense, net
	Interest expense	(366,584		)	(34,849		)	(3,221		)	87,039			(317,615		)
	Interest and investment income	27,750			57,268			7,494			(87,039		)	5,473
		(338,834		)	22,419			4,273			—			(312,142		)
	Other non-operating expense
	Net loss resulting from early retirement of debt	(21,975		)	(1,693		)	—			—			(23,668		)
	Income (loss) from continuing operations before income taxes	(1,037,594		)	(654,152		)	9,259			589,665			(1,092,822		)
	Provision for (benefit from) income taxes	(353,907		)	—			—			—			(353,907		)
	Income (loss) from continuing operations	(683,687		)	(654,152		)	9,259			589,665			(738,915		)
	Income from discontinued operations, net of tax	—			55,228			—			—			55,228
	Net Income (loss)	(683,687		)	(598,924		)	9,259			589,665			(683,687		)
	Less: Net income attributable to noncontrolling interest	(268		)	—			—			—			(268		)
Net Income (loss) attributable to Arch Coal, Inc.	$	(683,955	)	$	(598,924	)	$	9,259		$	589,665		$	(683,955	)
Total comprehensive income (loss)	$	(692,239	)	$	(604,903	)	$	9,259		$	595,644		$	(692,239	)
Condensed Consolidating Statements of Operations and Comprehensive Income
Year Ended December 31, 2011
	Parent/Issuer			Guarantor			Non-			Eliminations			Consolidated
				Subsidiaries			Guarantor
							Subsidiaries
	(In thousands)
Revenues	$	—		$	3,883,039		$	—		$	—		$	3,883,039
Costs, expenses and other													—
Cost of sales (exclusive of items shown separately below)	22,929			2,957,425			—			—			2,980,354
Depreciation, depletion and amortization	2,876			418,104			—			—			420,980
Amortization of acquired sales contracts, net	—			(22,069		)	—			—			(22,069		)
Change in fair value of coal derivatives and coal trading activities, net	—			(2,907		)	—			—			(2,907		)
Asset impairment and mine closure costs	—			7,316			—			—			7,316
Acquisition and transition costs	47,360			—			—			—			47,360
Selling, general and administrative expenses	74,591			43,572			3,527			(2,634		)	119,056
Other operating income, net	(23,306		)	10,811			(251		)	2,634			(10,112		)
	124,450			3,412,252			3,276			—			3,539,978
Loss from investment in subsidiaries	532,757			—			—			(532,757		)	—
Income (loss) from operations	408,307			470,787			(3,276		)	(532,757		)	343,061
Interest expense, net
Interest expense	(256,191		)	(46,218		)	(2,224		)	74,447			(230,186		)
Interest and investment income	15,935			55,041			6,780			(74,447		)	3,309
	(240,256		)	8,823			4,556			—			(226,877		)
Nonoperating expense	(49,490		)	(1,958		)	—			—			(51,448		)
Income (loss) from continuing operations before income taxes	118,561			477,652			1,280			(532,757		)	64,736
Provision for (benefit from) income taxes	(24,279		)	—			—			—			(24,279		)
Income (loss) from continuing operations	142,840			477,652			1,280			(532,757		)	89,015
Income from discontinued operations, net of tax	—			53,825			—			—			53,825
Net Income (loss)	142,840			531,477			1,280			(532,757		)	142,840
Less: Net income attributable to noncontrolling interest	(1,157		)	—			—			—			(1,157		)
Net Income (loss) attributable to Arch Coal, Inc.	$	141,683		$	531,477		$	1,280		$	(532,757	)	$	141,683
Total comprehensive income (loss)	$	141,240		$	537,561		$	1,280		$	(538,841	)	$	141,240
Schedule of Condensed Consolidating Balance Sheets [Table Text Block]	'
	Condensed Consolidating Balance Sheets
	December 31, 2013
		Parent/Issuer			Guarantor			Non-Guarantor			Eliminations			Consolidated
					Subsidiaries			Subsidiaries
		(In thousands)
	Assets
	Cash and cash equivalents	$	799,333		$	100,418		$	11,348		$	—		$	911,099
	Restricted cash	—			—			—			—			—
	Short term investments	248,414			—			—			—			248,414
	Receivables	14,177			23,018			197,015			(4,637		)	229,573
	Inventories	—			264,161			—			—			264,161
	Other	84,401			43,617			806			—			128,824
	Total current assets	1,146,325			431,214			209,169			(4,637		)	1,782,071
	Property, plant and equipment, net	24,851			6,709,398			37			—			6,734,286
	Investment in subsidiaries	7,741,589			—			—			(7,741,589		)	—
	Intercompany receivables				1,953,719			(181,095		)	(1,772,624		)	—
	Note receivable from Arch Western	675,000			—			—			(675,000		)	—
	Other	162,287			311,463			86			—			473,836
	Total other assets	8,578,876			2,265,182			(181,009		)	(10,189,213		)	473,836
	Total assets	$	9,750,052		$	9,405,794		$	28,197		$	(10,193,850	)	$	8,990,193
	Liabilities and Stockholders’ Equity
	Accounts payable	$	17,781		$	158,224		$	137		$	—		$	176,142
	Accrued expenses and other current liabilities	53,779			228,664			781			(4,637		)	278,587
	Current maturities of debt	28,882			4,611			—			—			33,493
	Total current liabilities	100,442			391,499			918			(4,637		)	488,222
	Long-term debt	5,099,833			18,169			—						5,118,002
	Intercompany payables	1,772,624			—			—			(1,772,624		)	—
	Note payable to Arch Coal	—			675,000			—			(675,000		)	—
	Asset retirement obligations	1,095			401,618			—			—			402,713
	Accrued pension benefits	7,797			(686		)	—			—			7,111
	Accrued postretirement benefits other than pension	12,079			27,176			—			—			39,255
	Accrued workers’ compensation	21,546			56,516			—			—			78,062
	Deferred income taxes	413,546			—			—			—			413,546
	Other noncurrent liabilities	67,841			121,794			398			—			190,033
	Total liabilities	7,496,803			1,691,086			1,316			(2,452,261		)	6,736,944
	Stockholders’ equity	2,253,249			7,714,708			26,881			(7,741,589		)	2,253,249
	Total liabilities and stockholders’ equity	$	9,750,052		$	9,405,794		$	28,197		$	(10,193,850	)	$	8,990,193
	Condensed Consolidating Balance Sheets
	December 31, 2012
		Parent/Issuer			Guarantor			Non-Guarantor			Eliminations			Consolidated
					Subsidiaries			Subsidiaries
		(In thousands)
	Assets
	Cash and cash equivalents	$	671,313		$	100,468		$	12,841		$	—		$	784,622
	Restricted cash	3,453			—			—			—			3,453
	Short term investments	234,305			—			—			—			234,305
	Receivables	49,281			40,452			247,171			(4,824		)	332,080
	Inventories	—			365,424			—			—			365,424
	Other	106,786			86,877			557			—			194,220
	Total current assets	1,065,138			593,221			260,569			(4,824		)	1,914,104
	Property, plant and equipment, net	27,476			7,309,550			72			—			7,337,098
	Investment in subsidiaries	8,254,508			—			—			(8,254,508		)	—
	Intercompany receivables	—			1,600,311			—			(1,600,311		)	—
	Note receivable from Arch Western	675,000			—			—			(675,000		)	—
	Other	187,171			568,314			90			—			755,575
	Total other assets	9,116,679			2,168,625			90			(10,529,819		)	755,575
	Total assets	$	10,209,293		$	10,071,396		$	260,731		$	(10,534,643	)	$	10,006,777
	Liabilities and Stockholders’ Equity
	Accounts payable	$	19,859		$	204,370		$	189		$	—		$	224,418
	Accrued expenses and other current liabilities	65,293			259,162			124			(4,824		)	319,755
	Current maturities of debt	32,054			842			—			—			32,896
	Total current liabilities	117,206			464,374			313			(4,824		)	577,069
	Long-term debt	5,061,925			23,954			—			—			5,085,879
Intercompany payables	1,367,739			—			232,572			(1,600,311		)	—
Note payable to Arch Coal	—			675,000			—			(675,000		)	—
Asset retirement obligations	1,646			408,059			—			—			409,705
Accrued pension benefits	33,456			34,174			—			—			67,630
Accrued postretirement benefits other than pension	13,953			31,133			—			—			45,086
Accrued workers’ compensation	25,323			56,306			—			—			81,629
Deferred income taxes	664,182			—			—			—			664,182
Other noncurrent liabilities	69,296			151,360			374			—			221,030
Total liabilities	7,354,726			1,844,360			233,259			(2,280,135		)	7,152,210
Stockholders’ equity	2,854,567			8,227,036			27,472			(8,254,508		)	2,854,567
Total liabilities and stockholders’ equity	$	10,209,293		$	10,071,396		$	260,731		$	(10,534,643	)	$	10,006,777
Schedule of Condensed Consolidating Statements of Cash Flows [Table Text Block]	'
	Condensed Consolidating Statements of Cash Flows
	Year Ended December 31, 2013
		Parent/Issuer			Guarantor			Non-Guarantor			Eliminations			Consolidated
					Subsidiaries			Subsidiaries
		(In thousands)
	Cash provided by (used in) operating activities	$	(632,060	)	$	637,193		$	50,609		$	—		$	55,742
	Investing Activities
	Capital expenditures	(3,320		)	(293,664		)	—			—			(296,984		)
	Additions to prepaid royalties	—			(14,947		)	—			—			(14,947		)
	Proceeds from dispositions of property, plant and equipment	—			10,790			—			—			10,790
	Proceeds from sales-leaseback transactions	—			34,919			—			—			34,919
	Proceeds from sale of Canyon Fuel	—			422,663			—			—			422,663
	Purchases of short term investments	(213,726		)	—			—			—			(213,726		)
	Proceeds from sales of short term investments	194,537			—			—			—			194,537
	Investments in and advances to affiliates	(5,451		)	(10,321		)	—			512			(15,260		)
	Change in restricted cash	3,453			—			—			—			3,453
	Cash provided by (used in) investing activities	(24,507		)	149,440			—			512			125,445
	Financing Activities
	Contributions from parent	—			512			—			(512		)	—
	Proceeds from term loan and senior notes	644,000			—			—			—			644,000
	Payments to retire debt	(628,660		)	(512		)	—			—			(629,172		)
	Payments on term loan	(17,250		)	—			—			—			(17,250		)
	Net payments on other debt	(6,324		)	—			—			—			(6,324		)
	Debt financing costs	(19,864		)	—			(625		)	—			(20,489		)
	Dividends paid	(25,475		)	—			—			—			(25,475		)
	Transactions with affiliates, net	838,160			(786,683		)	(51,477		)	—			—
	Cash provided by (used in) financing activities	784,587			(786,683		)	(52,102		)	(512		)	(54,710		)
	Increase (decrease) in cash and cash equivalents	128,020			(50		)	(1,493		)	—			126,477
	Cash and cash equivalents, beginning of period	671,313			100,468			12,841			—			784,622
	Cash and cash equivalents, end of period	$	799,333		$	100,418		$	11,348		$	—		$	911,099
	Condensed Consolidating Statements of Cash Flows
	Year Ended December 31, 2012
		Parent/Issuer			Guarantor			Non-Guarantor			Eliminations			Consolidated
					Subsidiaries			Subsidiaries
		(In thousands)
	Cash provided by (used in) operating activities	$	(571,576	)	$	781,551		$	122,829		$	—		$	332,804
	Investing Activities
	Change in restricted cash	6,869			—			—			—			6,869
	Capital expenditures	(4,424		)	(390,801		)	—			—			(395,225		)
	Proceeds from dispositions of property, plant and equipment	—			1,328			21,497			—			22,825
	Investments in and advances to affiliates	(6,287		)	(13,134		)	—			1,663			(17,758		)
	Purchases of short term investments	(236,862		)	—			—			—			(236,862		)
	Proceeds from sales of short term investments	1,754			—			—			—			1,754
	Purchase of noncontrolling interest	(17,500		)	—			—			—			(17,500		)
	Additions to prepaid royalties	—			(13,269		)	—			—			(13,269		)
	Cash provided by (used in) investing activities	(256,450		)	(415,876		)	21,497			1,663			(649,166		)
	Financing Activities
	Contributions from parent	—			1,663			—			(1,663		)	—
	Proceeds from term loan and senior notes	1,993,253			—			—			—			1,993,253
	Payments to retire debt	—			(452,934		)	—			—			(452,934		)
	Net decrease in borrowings under lines of credit and commercial paper program	(375,000		)	—			(106,300		)	—			(481,300		)
	Payments on term loan	(7,625		)	—			—			—			(7,625		)
	Net payments on other debt	(682		)	—			—			—			(682		)
	Debt financing costs	(50,022		)	—			(546		)	—			(50,568		)
	Dividends paid	(42,440		)	—			—			—			(42,440		)
	Issuance of common stock under incentive plans	5,131			—			—			—			5,131
	Transactions with affiliates, net	(84,651		)	110,639			(25,988		)	—			—
	Cash provided by (used in) financing activities	1,437,964			(340,632		)	(132,834		)	(1,663		)	962,835
	Increase in cash and cash equivalents	609,938			25,043			11,492			—			646,473
	Cash and cash equivalents, beginning of period	61,375			75,425			1,349			—			138,149
	Cash and cash equivalents, end of period	$	671,313		$	100,468		$	12,841		$	—		$	784,622
	Condensed Consolidating Statements of Cash Flows
	Year Ended December 31, 2011
	Parent/Issuer			Guarantor			Non-Guarantor			Eliminations			Consolidated
				Subsidiaries			Subsidiaries
	(In thousands)
Cash provided by (used in) operating activities	$	(187,039	)	$	998,082		$	(168,801	)	$	—		$	642,242
Investing Activities
Acquisition of ICG, net of cash acquired	(2,894,339		)	—			—			—			(2,894,339		)
Change in restricted cash	5,167			—			—			—			5,167
Capital expenditures	(12,809		)	(528,021		)	(106		)	—			(540,936		)
Proceeds from dispositions of property, plant and equipment	—			25,887			—			—			25,887
Investments in and advances to affiliates	(633,534		)	(33,553		)	—			605,178			(61,909		)
Additions to prepaid royalties	—			(29,957		)	—			—			(29,957		)
Consideration paid related to prior business acquisition	(829		)	—			—			—			(829		)
Cash provided by (used in) investing activities	(3,536,344		)	(565,644		)	(106		)	605,178			(3,496,916		)
Financing Activities
Contributions from parent	—			605,178			—			(605,178		)	—
Proceeds from the issuance of senior notes	2,000,000			—			—			—			2,000,000
Proceeds from the issuance of common stock, net	1,267,933			—			—			—			1,267,933
Payments to retire debt	—			(605,178		)	—			—			(605,178		)
Net decrease in borrowings under lines of credit and commercial paper program	375,000			(56,904		)	106,300			—			424,396
Net proceeds from other debt	5,334			—			—			—			5,334
Debt financing costs	(114,799		)	(16		)	(8		)	—			(114,823		)
Dividends paid	(80,748		)	—			—			—			(80,748		)
Issuance of common stock under incentive plans	2,316			—			—			—			2,316
Transactions with affiliates, net	316,009			(379,973		)	63,964			—			—
Cash provided by (used in) financing activities	3,771,045			(436,893		)	170,256			(605,178		)	2,899,230
Increase (decrease) in cash and cash equivalents	47,662			(4,455		)	1,349			—			44,556
Cash and cash equivalents, beginning of period	13,713			79,880			—			—			93,593
Cash and cash equivalents, end of period	$	61,375		$	75,425		$	1,349		$	—		$	138,149

Basis_of_Presentation_Narrativ

Basis of Presentation (Narrative) (Details) (USD $)	0 Months Ended	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Jul. 02, 2012	Jun. 30, 2012	Dec. 31, 2013	Dec. 31, 2011
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]	'	'	'	'
Number of mining complexes operated	'	4	'	'
number of mining complexes temporarily idled	'	'	1	'
Purchase of noncontrolling interest	$17,500	'	$0	$0

Accounting_Policies_Narrative_

Accounting Policies (Narrative) (Details) (USD $)	3 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statutory Accounting Practices	'	'	'	'
Interest Costs Capitalized	'	$15,900,000	$15,600,000	$1,900,000
Property, Plant and Equipment, Net	'	6,734,286,000	7,337,098,000	'
Deferred Finance Costs, Net	'	99,200,000	101,500,000	'
Deferred Finance Costs, Current, Net	'	19,700,000	17,300,000	'
Number of mining complexes operated	4	'	'	'
Exploration and Production Equipment [Member] | Minimum [Member]	'	'	'	'
Statutory Accounting Practices	'	'	'	'
Property, Plant and Equipment, Useful Life	'	'5 years	'	'
Exploration and Production Equipment [Member] | Maximum [Member]	'	'	'	'
Statutory Accounting Practices	'	'	'	'
Property, Plant and Equipment, Useful Life	'	'32 years	'	'
Building and Building Improvements [Member] | Minimum [Member]	'	'	'	'
Statutory Accounting Practices	'	'	'	'
Property, Plant and Equipment, Useful Life	'	'10 years	'	'
Building and Building Improvements [Member] | Maximum [Member]	'	'	'	'
Statutory Accounting Practices	'	'	'	'
Property, Plant and Equipment, Useful Life	'	'30 years	'	'
Mining Properties and Mineral Rights [Member]	'	'	'	'
Statutory Accounting Practices	'	'	'	'
Property, Plant and Equipment, Net	'	4,800,000,000	5,100,000,000	'
Mining Properties and Mineral Rights [Member] | Minimum [Member]	'	'	'	'
Statutory Accounting Practices	'	'	'	'
Lessee Leasing Arrangements, Operating Leases, Term of Contract	'	'10 years	'	'
Mining Properties and Mineral Rights [Member] | Maximum [Member]	'	'	'	'
Statutory Accounting Practices	'	'	'	'
Lessee Leasing Arrangements, Operating Leases, Term of Contract	'	'50 years	'	'
Capital Addition Purchase Commitments [Member]	'	'	'	'
Statutory Accounting Practices	'	'	'	'
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	'	60,400,000	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	'	75,800,000	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	'	60,400,000	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	'	$400,000	'	'

Discontinued_Operations_Narrat

Discontinued Operations (Narrative) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Discontinued Operations and Disposal Groups [Abstract]	'	'	'
Proceeds from sale of Canyon Fuel	$422,663	'	'

Discontinued_Operations_Schedu

Discontinued Operations (Schedule of Results of Discontinued Operations) (Details) (USD $)

3 Months Ended

7 Months Ended

12 Months Ended

In Thousands, except Per Share data, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Aug. 16, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Discontinued Operations and Disposal Groups [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

Total Revenues

'

'

'

'

'

'

'

'

$219,002

'

$390,912

$402,856

Income from discontinued operations before income taxes

'

'

'

'

'

'

'

'

32,167

'

75,418

70,515

Gain on sale

'

'

'

'

'

'

'

'

120,321

120,321

0

0

Less: income tax expense

'

'

'

'

'

'

'

'

49,092

'

20,190

16,690

Income from discontinued operations, including gain on sale - net of tax

$1,580

$79,404

$8,145

$14,267

$11,610

$21,078

$7,032

$15,508

$103,396

$103,396

$55,228

$53,825

Basic earnings per common share from discontinued operations

'

'

'

'

'

'

'

'

$0.49

'

$0.26

$0.28

Diluted earnings per common share from discontinued operations

'

'

'

'

'

'

'

'

$0.49

'

$0.26

$0.28

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Income (Loss) (Schedule of Accumulated Other Comprehensive Income (Loss)) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]	'	'
Balance at	($16,507)	($7,950)
Unrealized gains	54,585	-12,132
Amounts reclassified from accumulated other comprehensive income (loss)	-386	3,575
Balance at	37,692	-16,507
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	'	'
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]	'	'
Balance at	2,244	-4,729
Unrealized gains	168	4,320
Amounts reclassified from accumulated other comprehensive income (loss)	-1,847	2,653
Balance at	565	2,244
Accumulated Defined Benefit Plans Adjustment [Member]	'	'
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]	'	'
Balance at	-18,286	-4,676
Unrealized gains	48,482	-14,528
Amounts reclassified from accumulated other comprehensive income (loss)	916	918
Balance at	31,112	-18,286
Accumulated Net Unrealized Investment Gain (Loss) [Member]	'	'
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]	'	'
Balance at	-465	1,455
Unrealized gains	5,935	-1,924
Amounts reclassified from accumulated other comprehensive income (loss)	545	4
Balance at	$6,015	($465)

Accumulated_Other_Comprehensiv3

Accumulated Other Comprehensive Income (Loss) (Schedule of Reclassifications) (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenues	$719,386	$791,269	$766,332	$737,370	$867,034	$975,170	$965,685	$960,237	$3,014,357	$3,768,126	$3,883,039
Loss from continuing operations before income taxes	'	'	'	'	'	'	'	'	-1,080,726	-1,092,822	64,736
Benefit from income taxes	'	'	'	'	'	'	'	'	335,498	353,907	24,279
Net income (loss)	-371,214	-128,363	-72,206	-70,049	-295,423	45,751	-435,424	1,409	-641,832	-683,687	142,840
Reclassification out of accumulated other comprehensive income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Commodity Contract [Member]	'	'	'	'	'	'	'	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenues	'	'	'	'	'	'	'	'	2,886	'	'
Benefit from income taxes	'	'	'	'	'	'	'	'	-1,039	'	'
Net income (loss)	'	'	'	'	'	'	'	'	1,847	'	'
Reclassification out of accumulated other comprehensive income [Member] | Accumulated Defined Benefit Plans Adjustment [Member]	'	'	'	'	'	'	'	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Amortization of prior service credits	'	'	'	'	'	'	'	'	13,705	'	'
Amortization of actuarial gains (losses), net	'	'	'	'	'	'	'	'	-15,136	'	'
Loss from continuing operations before income taxes	'	'	'	'	'	'	'	'	-1,431	'	'
Benefit from income taxes	'	'	'	'	'	'	'	'	515	'	'
Net income (loss)	'	'	'	'	'	'	'	'	-916	'	'
Reclassification out of accumulated other comprehensive income [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]	'	'	'	'	'	'	'	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Interest and investment income	'	'	'	'	'	'	'	'	-852	'	'
Benefit from income taxes	'	'	'	'	'	'	'	'	307	'	'
Net income (loss)	'	'	'	'	'	'	'	'	($545)	'	'

Impairment_Charges_and_Mine_Cl2

Impairment Charges and Mine Closure Costs (Details) (USD $)

3 Months Ended

12 Months Ended

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Impaired Long-Lived Assets Held and Used [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Inventory Write-down

'

'

'

'

'

'

'

'

'

$2,600,000

'

'

Impairment of Long-Lived Assets Held-for-use

'

'

'

'

'

'

'

'

142,800,000

'

'

'

Severance Costs

'

'

'

'

'

'

'

'

'

12,300,000

'

'

Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements and Curtailments

'

'

'

'

'

'

'

'

'

-1,800,000

'

'

Restructuring and Related Cost, Incurred Cost

'

'

'

'

'

'

'

'

'

'

'

523,500,000

Asset impairment and mine closure costs

0

200,397,000

20,482,000

0

15,743,000

-2,144,000

525,583,000

0

220,879,000

539,182,000

7,316,000

'

Assets, Fair Value Disclosure, Nonrecurring

71,300,000

'

'

'

'

'

'

'

71,300,000

'

'

'

Productive Land [Member]

'

'

'

'

'

'

'

'

'

'

'

'

Impaired Long-Lived Assets Held and Used [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Impairment of Long-Lived Assets Held-for-use

'

'

'

'

'

'

'

'

'

403,300,000

'

'

Machinery and Equipment [Member]

'

'

'

'

'

'

'

'

'

'

'

'

Impaired Long-Lived Assets Held and Used [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Impairment of Long-Lived Assets Held-for-use

'

'

'

'

'

'

'

'

'

95,600,000

'

'

Mining Properties and Mineral Rights [Member]

'

'

'

'

'

'

'

'

'

'

'

'

Impaired Long-Lived Assets Held and Used [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Impairment of Intangible Assets, Finite-lived

'

'

'

'

'

'

'

'

'

$11,500,000

'

'

Goodwill_Narrative_Details

Goodwill (Narrative) (Details) (USD $)

3 Months Ended

12 Months Ended

In Thousands, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Goodwill [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Asset Impairment Charges

$265,423

'

'

'

$214,889

'

'

'

'

'

'

'

Goodwill

0

'

'

'

265,423

'

'

'

0

265,423

596,103

114,963

Goodwill, Impairment Loss

'

0

0

0

'

0

115,791

0

265,423

330,680

0

'

Black Thunder [Member]

'

'

'

'

'

'

'

'

'

'

'

'

Goodwill [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Goodwill, Impairment Loss

'

'

'

'

'

'

'

'

'

115,800

'

'

APP [Member]

'

'

'

'

'

'

'

'

'

'

'

'

Goodwill [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Goodwill, Impairment Loss

'

'

'

'

'

'

'

'

$265,423

$214,900

'

'

Goodwill_Schedule_of_Goodwill_

Goodwill (Schedule of Goodwill) (Details) (USD $)	3 Months Ended						12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Goodwill [Roll Forward]	'	'	'	'	'	'	'	'	'
Goodwill, Beginning Balance	'	'	$265,423	'	'	$596,103	$265,423	$596,103	$114,963
Payments for (Proceeds from) Previous Acquisition	'	'	'	'	'	'	'	0	829
Goodwill, Impairment Loss	0	0	0	0	-115,791	0	-265,423	-330,680	0
Goodwill, Ending Balance	'	'	'	'	'	'	0	265,423	596,103
Black Thunder [Member]	'	'	'	'	'	'	'	'	'
Goodwill [Roll Forward]	'	'	'	'	'	'	'	'	'
Goodwill, Impairment Loss	'	'	'	'	'	'	'	-115,800	'
Parent [Member]	'	'	'	'	'	'	'	'	'
Goodwill [Roll Forward]	'	'	'	'	'	'	'	'	'
Payments for (Proceeds from) Previous Acquisition	'	'	'	'	'	'	'	'	829
Goodwill, Acquired During Period	'	'	'	'	'	'	'	'	480,311
ICG [Member]	'	'	'	'	'	'	'	'	'
Goodwill [Roll Forward]	'	'	'	'	'	'	'	'	'
Goodwill, Impairment Loss	'	'	'	'	'	'	'	($330,680)	'

Inventories_Details

Inventories (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Inventory Disclosure [Abstract]	'	'
Coal	$117,531,000	$180,917,000
Repair parts and supplies	137,497,000	172,139,000
Work-in-process	9,133,000	12,368,000
Inventories	264,161,000	365,424,000
Allowance for slow-moving and obsolete inventories	$8,400,000	'

Investments_in_AvailableforSal2

Investments in Available-for-Sale Securities (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]	'	'
Cost Basis	$255,046	$240,382
Gross Unrealized Gains	13,678	2,706
Gross Unrealized Losses	-4,281	-3,436
Fair Value	264,443	239,652
Total Investments	248,414	234,305
US Government Agencies Debt Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Cost Basis	65,002	146,993
Available-for-sale Debt Securities Gross Unrealized Gain	12	2
Available-for-sale Debt Securities, Gross Unrealized Loss	-75	-412
Fair Value	64,938	146,583
Corporate Debt Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Cost Basis	184,773	88,118
Available-for-sale Debt Securities Gross Unrealized Gain	6	'
Available-for-sale Debt Securities, Gross Unrealized Loss	-1,304	-396
Fair Value	183,476	87,722
Equity Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Cost Basis	5,271	5,271
Available-for-sale Equity Securities, Gross Unrealized Gain	13,660	2,704
Available-for-sale Equity Securities, Gross Unrealized Loss	-2,902	-2,628
Fair Value	16,029	5,347
Short-term Investments [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
U.S. government and agency securities	64,938	146,583
Corporate notes and bonds	183,476	87,722
Total Investments	248,414	234,305
Other Assets [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Equity securities	$16,029	$5,347

Investments_in_AvailableforSal3

Investments in Available-for-Sale Securities (Narrative) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Available-for-sale Securities [Abstract]	'	'
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$164.30	$223.30
Available-for-sale Securities, Continuous Unrealized Loss Position, Greater than Twelve Months, Fair Value	$48.70	$0.40

Equity_Investments_and_Members2

Equity Investments and Membership Interests in Joint Ventures (Narrative) (Details) (USD $)

3 Months Ended

12 Months Ended

3 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

Sep. 30, 2013

Dec. 31, 2013

Dec. 31, 2011

Dec. 31, 2013

Sep. 30, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2011

Jan. 31, 2011

Dec. 31, 2013

Dec. 31, 2011

Jul. 31, 2011

Dec. 31, 2013

Knight Hawk [Member]

DKRW [Member]

DKRW [Member]

DKRW [Member]

DTA [Member]

Tenaska [Member]

Tenaska [Member]

Millennium [Member]

Millennium [Member]

Millennium [Member]

Tongue River [Member]

Tongue River [Member]

Tongue River [Member]

Equity Method Investee [Member]

Schedule of Equity Method Investments [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Equity Method Investment, Ownership Percentage

'

'

'

49.00%

'

24.00%

'

21.88%

35.00%

'

'

'

38.00%

'

'

35.00%

'

Due from Related Parties

'

'

'

'

'

'

$38,700,000

'

'

'

'

'

'

'

'

'

'

Other than Temporary Impairment Losses, Investments

'

'

'

'

'

-57,700,000

'

'

-20,500,000

'

'

'

'

'

'

'

'

Impairment of equity investment

'

-28,947,000

'

'

-13,683,000

'

'

'

-15,264,000

'

'

'

'

'

'

'

'

Provision for Loan, Lease, and Other Losses

-5,200,000

'

'

'

-44,000,000

'

'

'

'

'

'

'

'

'

'

'

'

Investments in affiliates

'

'

43,489,000

'

'

'

'

'

'

5,500,000

'

25,000,000

'

'

12,989,000

'

'

Future development costs, maximum limit

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$58,500,000

Equity_Investments_and_Members3

Equity Investments and Membership Interests in Joint Ventures (Schedule of Equity Method Investments) (Details) (USD $)	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]	'	'	'	'
Balance at December 31, 2012	'	$242,215	$225,605	$177,451
Investments in affiliates	'	'	'	43,489
Advances to (distributions from) affiliates, net	'	788	7,690	-6,646
Equity in comprehensive income (loss)	'	-7,400	-8,920	-11,311
Impairment of equity investment	'	-28,947	'	'
Balance at December 31, 2013	'	221,456	242,215	225,605
Knight Hawk [Member]	'	'	'	'
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]	'	'	'	'
Balance at December 31, 2012	'	149,063	135,225	131,250
Advances to (distributions from) affiliates, net	'	-13,536	-7,151	-16,621
Equity in comprehensive income (loss)	'	-17,279	-20,989	-20,596
Impairment of equity investment	'	'	'	'
Balance at December 31, 2013	'	152,806	149,063	135,225
DKRW [Member]	'	'	'	'
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]	'	'	'	'
Balance at December 31, 2012	'	15,515	19,715	21,961
Advances to (distributions from) affiliates, net	'	'	'	'
Equity in comprehensive income (loss)	'	1,832	4,200	2,246
Impairment of equity investment	-13,683	'	'	'
Balance at December 31, 2013	'	'	15,515	19,715
DTA [Member]	'	'	'	'
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]	'	'	'	'
Balance at December 31, 2012	'	15,462	16,086	14,472
Advances to (distributions from) affiliates, net	'	3,644	4,335	6,498
Equity in comprehensive income (loss)	'	4,969	4,959	4,884
Impairment of equity investment	'	'	'	'
Balance at December 31, 2013	'	14,137	15,462	16,086
Tenaska [Member]	'	'	'	'
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]	'	'	'	'
Balance at December 31, 2012	'	15,264	15,266	9,768
Investments in affiliates	'	'	'	5,500
Advances to (distributions from) affiliates, net	'	'	'	'
Equity in comprehensive income (loss)	'	'	2	2
Impairment of equity investment	'	-15,264	'	'
Balance at December 31, 2013	'	'	15,264	15,266
Millennium [Member]	'	'	'	'
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]	'	'	'	'
Balance at December 31, 2012	'	32,214	26,324	'
Investments in affiliates	'	'	'	25,000
Advances to (distributions from) affiliates, net	'	6,476	8,798	3,477
Equity in comprehensive income (loss)	'	2,796	2,908	2,153
Impairment of equity investment	'	'	'	'
Balance at December 31, 2013	'	35,894	32,214	26,324
Tongue River [Member]	'	'	'	'
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]	'	'	'	'
Balance at December 31, 2012	'	14,697	12,989	'
Investments in affiliates	'	'	'	12,989
Advances to (distributions from) affiliates, net	'	4,004	1,708	'
Equity in comprehensive income (loss)	'	282	'	'
Impairment of equity investment	'	'	'	'
Balance at December 31, 2013	'	18,419	14,697	12,989
Other Affiliates [Member]	'	'	'	'
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]	'	'	'	'
Balance at December 31, 2012	'	'	'	'
Advances to (distributions from) affiliates, net	'	200	'	'
Equity in comprehensive income (loss)	'	'	'	'
Impairment of equity investment	'	'	'	'
Balance at December 31, 2013	'	$200	'	'

Equity_Investments_and_Members4

Equity Investments and Membership Interests in Joint Ventures (Summarized Financial Information of Equity Method Investments) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Equity Method Investments and Joint Ventures [Abstract]	'	'	'
Equity Method Investment, Summarized Financial Information, Revenue	$208,289	$190,661	$184,358
Equity Method Investment, Summarized Financial Information, Gross Profit (Loss)	10,234	15,308	19,495
Equity Method Investment, Summarized Financial Information, Income (Loss) from Continuing Operations before Extraordinary Items	6,574	8,898	13,180
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	-397	641	6,788
Equity Method Investment, Summarized Financial Information, Current Assets	52,413	78,961	'
Equity Method Investment, Summarized Financial Information, Noncurrent Assets	398,495	387,884	'
Equity Method Investment, Summarized Financial Information, Assets	450,908	466,845	'
Equity Method Investment, Summarized Financial Information, Current Liabilities	31,243	57,403	'
Equity Method Investment, Summarized Financial Information, Noncurrent Liabilities	131,445	128,489	'
Equity Method Investment Summarized Financial Information, Equity	287,903	280,690	'
Equity Method Investment, Summarized Financial Information, Noncontrolling Interest	317	263	'
Equity Method Investment, Summarized Financial Information, Liabilities and Equity	$450,908	$466,845	'

Acquired_Sales_Contracts_Narra

Acquired Sales Contracts (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2013
Supply Commitment [Line Items]	'	'
Impairment of Intangible Assets, Finite-lived	$15,700,000	'
Acquired fair value, Assets	131,819,000	131,819,000
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	'	21,500,000
Finite-Lived Intangible Assets, Amortization Expense, Year Two	'	6,700,000
Finite-Lived Intangible Assets, Amortization Expense, Year Three	'	2,800,000
Finite-Lived Intangible Assets, Amortization Expense, Year Four	'	3,300,000
Finite-Lived Intangible Assets, Amortization Expense, Year Five	'	3,100,000
imparment of intangible asset [Member]	'	'
Supply Commitment [Line Items]	'	'
Acquired fair value, Assets	$17,500,000	'

Acquired_Sales_Contracts_Sched

Acquired Sales Contracts (Schedule of Acquired Sales Contracts) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]	'	'
Acquired fair value, Assets	$131,819	$131,819
Acquired fair value, Liabilities	166,697	166,697
Accumulated amortization, Asset	-129,449	-123,776
Accumulated amortization, Liabilities	-120,367	-105,237
Total, Assets	2,370	8,043
Total, Liabilities	46,330	61,460
Net total, Liabilites	-43,960	-53,417
Coal Supply Agreement, Liabilities	14,373	14,038
Other Current Assets [Member]	'	'
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]	'	'
Coal supply agreement, Assets	1,324	5,651
Accrued Liabilities [Member]	'	'
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]	'	'
Coal Supply Agreement, Liabilities	14,373	14,038
Other Assets [Member]	'	'
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]	'	'
Coal supply agreement, Assets	1,046	2,392
Other Noncurrent Liabilities [Member]	'	'
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]	'	'
Coal Supply Agreement, Liabilities	$31,957	$47,422

Derivatives_Narrative_Details

Derivatives (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Derivative [Line Items]	'	'	'
Gain (Loss) on Components Excluded from Assessment of Price Risk Hedge Effectiveness	'	'	$8.20
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	'	'	5.2
Current asset (liability) for the right to reclaim cash collateral	2.2	16.2	'
Net unrealized and realized gains (losses) related to trading portfolio	4.9	8.3	'
Gain on derivative contracts designated as hedge instruments in cash flow hedges to be reclassified from OCI into earnings during the next twelve months	0.8	'	'
Year One [Member]	'	'	'
Derivative [Line Items]	'	'	'
Value of trading portfolio realized	9.6	'	'
Diesel Purchases [Member] | Year One [Member]	'	'	'
Derivative [Line Items]	'	'	'
Percent of expected requirements covered	91.00%	'	'
Diesel Purchases [Member] | Year Two [Member]	'	'	'
Derivative [Line Items]	'	'	'
Percent of expected requirements covered	10.00%	'	'
Diesel Purchases [Member] | Heating Oil [Member]	'	'	'
Derivative [Line Items]	'	'	'
Quantities under derivative contracts	63,000,000	'	'
Diesel Purchases [Member] | Minimum [Member]	'	'	'
Derivative [Line Items]	'	'	'
Gallons of diesel fuel purchased annually	57,000,000	'	'
Diesel Purchases [Member] | Maximum [Member]	'	'	'
Derivative [Line Items]	'	'	'
Gallons of diesel fuel purchased annually	67,000,000	'	'
Diesel Usage Fuel Surcharges [Member] | Heating Oil [Member] | Year Two [Member]	'	'	'
Derivative [Line Items]	'	'	'
Quantities under derivative contracts	5,100,000	'	'
Heating Oil [Member] | Derivative [Member]	'	'	'
Derivative [Line Items]	'	'	'
Other Operating Income	'	'	$14.90

Derivatives_Schedule_of_Price_

Derivatives (Schedule of Price Risk Derivatives) (Details)	Dec. 31, 2013
Coal Sales [Member]	'
Derivative [Line Items]	'
Derivatives Held	5,745,000
Coal Purchases [Member]	'
Derivative [Line Items]	'
Derivatives Held	1,561,000
Year One [Member] | Coal Sales [Member]	'
Derivative [Line Items]	'
Derivatives Held	4,845,000
Year One [Member] | Coal Purchases [Member]	'
Derivative [Line Items]	'
Derivatives Held	1,561,000
Year Two [Member] | Coal Sales [Member]	'
Derivative [Line Items]	'
Derivatives Held	900,000
Year Two [Member] | Coal Purchases [Member]	'
Derivative [Line Items]	'
Derivatives Held	0

Derivatives_Disclosure_of_Fair

Derivatives (Disclosure of Fair Value of Derivatives) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Derivative [Line Items]	'	'
Derivative Assets	$67,681	$54,863
Derivative Liabilities	-47,739	-24,285
Effect of counterparty netting in derivative assets	-47,727	-22,548
Effect of counterparty netting in derivative liabilities	47,727	22,548
Net derivative assets as classified in the balance sheet	19,954	32,315
Net derivative liabilities as classified in the balance sheet	-12	-1,737
Net derivatives as classified in the balance sheet	19,942	30,578
Designated as Hedging Instrument [Member] | Coal [Member]	'	'
Derivative [Line Items]	'	'
Derivative Assets	909	3,277
Derivative Liabilities	-26	-10
Not Designated as Hedging Instrument [Member]	'	'
Derivative [Line Items]	'	'
Derivative Assets	66,772	51,586
Derivative Liabilities	-47,713	-24,275
Not Designated as Hedging Instrument [Member] | Heating Oil-Diesel Purchases [Member]	'	'
Derivative [Line Items]	'	'
Derivative Assets	4,681	7,379
Derivative Liabilities	'	'
Not Designated as Hedging Instrument [Member] | Heating Oil-Fuel Surchages [Member]	'	'
Derivative [Line Items]	'	'
Derivative Assets	422	1,961
Derivative Liabilities	'	'
Not Designated as Hedging Instrument [Member] | Coal Held for Trading Purposes [Member]	'	'
Derivative [Line Items]	'	'
Derivative Assets	55,327	17,403
Derivative Liabilities	-45,763	-16,933
Not Designated as Hedging Instrument [Member] | Coal [Member]	'	'
Derivative [Line Items]	'	'
Derivative Assets	6,342	24,843
Derivative Liabilities	($1,950)	($7,342)

Derivatives_Net_Derivatives_as

Derivatives (Net Derivatives as Reflected on the Balance Sheets) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Derivatives, Fair Value [Line Items]	'	'
Net derivatives as classified in the balance sheet	$19,942	$30,578
Other Current Assets [Member] | Heating Oil [Member]	'	'
Derivatives, Fair Value [Line Items]	'	'
Net derivatives as classified in the balance sheet	5,103	9,340
Coal Derivative Assets [Member] | Coal [Member]	'	'
Derivatives, Fair Value [Line Items]	'	'
Net derivatives as classified in the balance sheet	14,851	22,975
Coal Derivative Liabilities [Member] | Coal [Member]	'	'
Derivatives, Fair Value [Line Items]	'	'
Net derivatives as classified in the balance sheet	($12)	($1,737)

Derivatives_Effects_of_Derivat

Derivatives (Effects of Derivatives on Measures of Financial Performance) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Derivative Instruments, Gain (Loss) [Line Items]	'		'		'
Gain (Loss) Recognized in OCI (Effective Portion)	$188,000		$5,250,000		$2,914,000
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	2,981,000		2,675,000		1,572,000
Coal derivative settlements, non-hedging	32,534,000		43,990,000		-7,000
Coal Sales [Member]	'		'		'
Derivative Instruments, Gain (Loss) [Line Items]	'		'		'
Gain (Loss) Recognized in OCI (Effective Portion)	-338,000	[1]	7,690,000	[1]	4,923,000	[1]
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	3,664,000	[1]	2,675,000	[1]	1,572,000	[1]
Coal Purchases [Member]	'		'		'
Derivative Instruments, Gain (Loss) [Line Items]	'		'		'
Gain (Loss) Recognized in OCI (Effective Portion)	526,000	[2]	-2,440,000	[2]	-2,009,000	[2]
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	-683,000	[2]	'	[2]	'	[2]
Coal [Member]	'		'		'
Derivative Instruments, Gain (Loss) [Line Items]	'		'		'
Unrealized Gain (Loss) on Derivatives	-12,700,000	[3]	8,272,000	[3]	6,438,000	[3]
Coal derivative settlements, non-hedging	32,534,000	[4]	43,990,000	[4]	-7,000	[4]
Heating Oil-Diesel Purchases [Member]	'		'		'
Derivative Instruments, Gain (Loss) [Line Items]	'		'		'
Realized Gains (Losses)	-9,791,000	[4]	-22,281,000	[4]	-2,906,000	[4]
Heating Oil-Fuel Surchages [Member]	'		'		'
Derivative Instruments, Gain (Loss) [Line Items]	'		'		'
Realized Gains (Losses)	-947,000	[4]	-2,209,000	[4]	'	[4]
Heating Oil [Member]	'		'		'
Derivative Instruments, Gain (Loss) [Line Items]	'		'		'
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	'		'		1,300,000
Derivative [Member] | Heating Oil [Member]	'		'		'
Derivative [Line Items]	'		'		'
Other Operating Income	'		'		$14,900,000
[1]	Revenues
[2]	Cost of sales
[3]	Change in fair value of coal derivatives and coal trading activities, net
[4]	Other operating income, net

Accrued_Expenses_and_Other_Cur2

Accrued Expenses and Other Current Liabilities (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Accrued Expenses and Other Current Liabilities [Abstract]	'	'
Payroll and employee benefits	$67,621	$72,405
Taxes other than income taxes	114,664	121,029
Interest	18,528	42,413
Acquired sales contracts	14,373	14,038
Workers’ compensation	12,434	10,371
Asset retirement obligations	24,940	38,920
Other	26,015	18,842
Accrued Liabilities, Current	$278,575	$318,018

Debt_and_Financing_Arrangement2

Debt and Financing Arrangements (Narrative) (Details) (USD $)

1 Months Ended

12 Months Ended

12 Months Ended

0 Months Ended

12 Months Ended

0 Months Ended

3 Months Ended

12 Months Ended

52 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

0 Months Ended

1 Months Ended

0 Months Ended

0 Months Ended

6 Months Ended

12 Months Ended

29-May-12

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 17, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 17, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Nov. 21, 2012

12-May-12

Sep. 30, 2012

Dec. 31, 2013

Apr. 30, 2018

Dec. 31, 2013

Dec. 17, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Jun. 14, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Jun. 14, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

12-May-12

29-May-12

Dec. 31, 2012

1-May-12

30-May-12

Jul. 14, 2011

Jun. 30, 2011

Jun. 30, 2011

Jun. 30, 2011

Jun. 30, 2011

Dec. 31, 2013

Dec. 31, 2012

8.00% Senior Secured Notes due 2019 [Member]

8.00% Senior Secured Notes due 2019 [Member]

8.00% Senior Secured Notes due 2019 [Member]

8.00% Senior Secured Notes due 2019 [Member]

8.00% Senior Secured Notes due 2019 [Member]

8.00% Senior Secured Notes due 2019 [Member]

8.75% Senior Notes Due 2016 [Member]

8.75% Senior Notes Due 2016 [Member]

8.75% Senior Notes Due 2016 [Member]

8.75% Senior Notes Due 2016 [Member]

Line of Credit [Member]

Line of Credit [Member]

Line of Credit [Member]

Line of Credit [Member]

Term Loan Due 2018 [Member]

Term Loan Due 2018 [Member]

Term Loan Due 2018 [Member]

Term Loan Due 2018 [Member]

Term Loan Due 2018 [Member]

Loans Payable [Member]

Loans Payable [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

9.875% Senior Notes Due 2019 [Member]

9.875% Senior Notes Due 2019 [Member]

9.875% Senior Notes Due 2019 [Member]

9.875% Senior Notes Due 2019 [Member]

9.875% Senior Notes Due 2019 [Member]

9.875% Senior Notes Due 2019 [Member]

7.25% Senior Notes Due 2020 [Member]

7.25% Senior Notes Due 2020 [Member]

7.25% Senior Notes Due October 10, 2020 [Member]

7.25% Senior Notes Due October 10, 2020 [Member]

7.25% Senior Notes Due October 10, 2020 [Member]

7.25% Senior Notes Due October 10, 2020 [Member]

7.25% Senior Notes Due October 10, 2020 [Member]

2019 and 2021 notes [Member]

7.00% Senior Notes Due 2019 [Member]

7.00% Senior Notes Due 2019 [Member]

7.00% Senior Notes Due 2019 [Member]

7.00% Senior Notes Due 2019 [Member]

7.00% Senior Notes Due 2019 [Member]

7.00% Senior Notes Due 2019 [Member]

7.00% Senior Notes Due 2019 [Member]

7.25% Senior Notes Due 2021 [Member]

7.25% Senior Notes Due 2021 [Member]

7.25% Senior Notes Due 2021 [Member]

7.25% Senior Notes Due 2021 [Member]

7.25% Senior Notes Due 2021 [Member]

7.25% Senior Notes Due 2021 [Member]

7.25% Senior Notes Due 2021 [Member]

7.25% Senior Notes Due 2021 [Member]

6.75% Senior Notes Due 2013 [Member]

6.75% Senior Notes Due 2013 [Member]

6.75% Senior Notes Due 2013 [Member]

Six Point Seven Five Percentage Senior Notes Due Two Thousand Thirteen [Member]

Six Point Seven Five Percentage Senior Notes Due Two Thousand Thirteen [Member]

9.125% Senior Notes Due 2018 [Member]

4.00% Convertible Senior Notes Due 2017 [Member]

4.00% and 9.00% Convertible Senior Notes [Member]

9.00% Convertible Senior Notes Due 2012 [Member]

ICG Debt [Member]

Senior Notes [Member]

Senior Notes [Member]

Redeemable between January 15, 2016 and January 14, 2017 [Member]

Redeemable between January 15, 2017 and January 14, 2018 [Member]

Redeemable on or after January 15, 2018 [Member]

Minimum [Member]

Maximum [Member]

Redeemable between December 15, 2016 and December 14, 2017 [Member]

Redeemable between December 15, 2017 and December 14, 2018 [Member]

On or after December 15, 2018 [Member]

Prior to December 15, 2015 [Member]

Redeemable between October 1, 2015 and September 30, 2016 [Member]

Redeemable between October 1, 2016 and September 30, 2017 [Member]

Redeemable between October 1, 2017 and September 30, 2018 [Member]

Redeemable on or after October 1, 2018 [Member]

Prior to June 15, 2015 [Member]

Redeemable between June 15, 2015 and June 14, 2016 [Member]

Redeemable between June 15, 2016 and June 14, 2017 [Member]

June 15, 2017 and Beyond [Member]

Prior to June 15, 2016 [Member]

Redeemable between June 15, 2016 and June 14, 2017 [Member]

Redeemable between June 15, 2017 and June 14, 2018 [Member]

Redeemable between June 15, 2018 and June 14, 2019 [Member]

June 15, 2019 and Beyond [Member]

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Senior notes interest rate

'

'

'

'

8.00%

'

'

'

'

'

'

8.75%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

9.88%

'

'

'

'

'

7.25%

'

'

'

'

'

'

'

'

'

'

'

'

7.00%

'

7.25%

'

'

'

'

'

'

'

'

'

'

'

'

'

4.00%

'

9.00%

'

'

'

Senior Notes

'

'

'

'

$350,000,000

'

$0

'

'

'

'

$0

$590,999,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$362,358,000

$360,042,000

'

'

'

'

$500,000,000

$500,000,000

'

'

'

'

'

'

'

'

'

'

'

$1,000,000,000

$1,000,000,000

$1,000,000,000

$1,000,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

298,500,000

'

1,700,000

54,000,000

'

'

Repayments of Long-term Debt

'

'

'

'

'

'

'

'

'

'

'

'

'

-628,700,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

308,000,000

'

'

'

'

'

'

'

'

'

'

Debt Instrument, Frequency of Periodic Payment

'

'on January 15 and July 15 of each year

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'Quarterly

'

'

'

'

'

'

'

'

'

'

'

'

'

' Interest is payable on the 2020 Notes on April 1 and October 1 of each year

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Instrument, Date of First Required Payment

'

15-Jul-14

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Instrument, Basis Spread on Variable Rate

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Instrument, Face Amount

'

'

'

'

'

350,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,925,125,000

300,000,000

'

'

375,000,000

'

'

'

'

'

500,000,000

'

'

'

'

'

'

'

1,000,000,000

'

'

'

'

'

'

'

'

1,000,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Instrument, Discounted Percentage From Face Amount

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

98.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Available borrowing capacity under lines of credit

'

253,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Line of Credit Facility, Unused Capacity, Commitment Fee Percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.50%

0.75%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Line of Credit Facility, Expiration Date

'

9-Dec-14

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Instrument, Unused Borrowing Capacity, Amount

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

250,000,000

350,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Proceeds from Issuance of Secured Debt

'

294,000,000

1,633,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

300,000,000

1,400,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Instrument, Discount (Premium), Percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1.00%

'

'

'

'

'

95.93%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Instrument, Periodic Payment, Principal

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

3,500,000

4,125,000

4,875,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,850,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1.25%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

CallPremium

'

'

'

'

'

'

'

104.00%

102.00%

100.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

104.94%

102.47%

100.00%

109.88%

'

'

'

0.00%

102.42%

101.21%

100.00%

'

'

107.00%

103.50%

101.75%

100.00%

'

'

'

'

'

107.25%

103.63%

102.42%

101.21%

100.00%

'

'

'

'

'

'

'

'

'

'

'

'

PercentageOfMaximumRedemptionAggregatePrincipalAmountFromEquityProceeds

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

35.00%

'

'

'

'

'

'

'

'

'

'

'

'

35.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Extinguishment of Debt, Amount

'

'

'

'

'

'

'

'

'

'

600,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

450,000,000

'

'

304,000,000

'

251,400,000

'

'

'

'

'

'

Redemption Premium

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Cash paid during the year for interest

'

380,389,000

310,241,000

213,697,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5,200,000

'

'

'

'

'

'

Debt Instrument, Repurchase Amount

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

146,000,000

'

'

'

'

'

'

'

Debt Instrument, Convertible, Beneficial Conversion Feature

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2,614.68

'

2,392.73

'

'

'

PrincipalAmountIncrementForConversion

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,000

'

'

'

'

Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months

'

33,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Long-term Debt, Maturities, Repayments of Principal in Year Two

'

24,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Long-term Debt, Maturities, Repayments of Principal in Year Three

'

24,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Long-term Debt, Maturities, Repayments of Principal in Year Four

'

23,700,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Long-term Debt, Maturities, Repayments of Principal in Year Five

'

1,900,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Line of Credit Facility, Covenant Terms

'

'Terms of the Company's credit facilities and leases contain financial and other covenants that limit the ability of the Company to, among other things, acquire, dispose, merge or consolidate assets; incur additional debt; pay dividends and make distributions or repurchase stock; make investments; create liens; issue and sell capital stock of subsidiaries; enter into restrictions affecting the ability of restricted subsidiaries to make distributions, loans or advances to the Company; engage in transactions with affiliates and enter into sale and leaseback transactions. In addition, the covenants require the Company to pledge assets to collateralize the revolving credit and term loan facilities. The assets pledged include equity interests in wholly‑owned subsidiaries, certain real property interests, accounts receivable and inventory of the Company. Failure by the Company to comply with such covenants could result in an event of default, which, if not cured or waived, could have a material adverse effect on the Company.

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Payments of Financing Costs

'

20,489,000

50,568,000

114,823,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Related Commitment Fees and Debt Issuance Costs

'

0

0

49,490,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Write off of Deferred Debt Issuance Cost

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,900,000

23,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5,400,000

1,100,000

Write Off Of Unamortized Discount

'

6,900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

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Debt Instrument, Unamortized Premium

'

'

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-800,000

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Net loss resulting from early retirement and refinancing of debt

'

($42,921,000)

($23,668,000)

($1,958,000)

'

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'

Debt_and_Financing_Arrangement3

Debt and Financing Arrangements (Debt) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Debt Instrument [Line Items]	'	'
Other	$32,162	$40,350
Total	5,151,495	5,118,775
Current maturities of debt	33,493	32,896
Long-term debt	5,118,002	5,085,879
Loans Payable [Member]	'	'
Debt Instrument [Line Items]	'	'
Term loan due 2018 ($1.93 billion and $1.65 billion face value, respectively)	1,906,975	1,627,384
8.75% Senior Notes Due 2016 [Member]	'	'
Debt Instrument [Line Items]	'	'
Senior notes	0	590,999
7.00% Senior Notes Due 2019 [Member]	'	'
Debt Instrument [Line Items]	'	'
Senior notes	1,000,000	1,000,000
8.00% Senior Secured Notes due 2019 [Member]	'	'
Debt Instrument [Line Items]	'	'
Senior notes	350,000	0
9.875% Senior Notes Due 2019 [Member]	'	'
Debt Instrument [Line Items]	'	'
Senior notes	362,358	360,042
7.25% Senior Notes Due 2020 [Member]	'	'
Debt Instrument [Line Items]	'	'
Senior notes	500,000	500,000
7.25% Senior Notes Due 2021 [Member]	'	'
Debt Instrument [Line Items]	'	'
Senior notes	$1,000,000	$1,000,000

Taxes_Narrative_Details

Taxes (Narrative) (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2008
Operating Loss Carryforwards [Line Items]	'	'	'	'	'	'
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	'	$31,789,000	$31,150,000	$8,798,000	$4,418,000	'
Stock options and other equity based compensation, tax expense (benefit)	'	1,500,000	300,000	-400,000	'	'
Operating loss carryforwards	'	1,800,000,000	'	'	'	145,100,000
Tax credit carryforward	'	127,000,000	'	'	'	'
Increase (decrease) in valuation allowance	'	8,700,000	31,800,000	2,100,000	'	'
Interest and penalties accrued related to unrecognized tax benefits	'	1,300,000	1,000,000	'	'	'
Interest and penalties recognized	'	300,000	200,000	200,000	'	'
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0	'	'	'	'	'
Payments for (Proceeds from) Previous Acquisition	'	'	$0	$829,000	'	'

Taxes_Schedule_of_Components_o

Taxes (Schedule of Components of Income Tax) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Taxes [Abstract]	'	'	'
Current Federal Tax Expense (Benefit)	$0	($20,022)	($24,449)
Current State and Local Tax Expense (Benefit)	-647	575	1,072
Current Income Tax Expense (Benefit)	-647	-19,447	-23,377
Deferred Federal Income Tax Expense (Benefit)	-318,956	-341,486	1,544
Deferred State and Local Income Tax Expense (Benefit)	-15,895	7,026	-2,446
Deferred Income Tax Expense (Benefit)	-334,851	-334,460	-902
Provision for (benefit from) income taxes	($335,498)	($353,907)	($24,279)

Taxes_Schedule_of_Effective_In

Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Taxes [Abstract]	'	'	'
Income tax expense statutory rate	($378,463)	($382,581)	$22,253
Percentage depletion allowance	-15,796	-33,654	-53,156
Income Tax Reconciliation, Nondeductible Expense, Impairment Losses	70,301	56,916	'
State taxes, net of effect of federal taxes	-25,265	-24,231	-3,790
Change in valuation allowance	8,659	31,832	2,416
Other, net	5,066	-2,189	7,998
Provision for (benefit from) income taxes	($335,498)	($353,907)	($24,279)

Taxes_Schedule_of_Deferred_Tax

Taxes (Schedule of Deferred Tax Assets And Liabilities) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Taxes [Abstract]	'	'
Alternative Minimum Tax Credit Carryforwards	$660,916	$496,330
Net Operating Loss Carryforwards	126,755	150,014
Reclamation and mine closure	113,843	104,570
Deferred Tax Assets, Goodwill and Intangible Assets	52,636	43,839
Acquired sales contracts	33,392	38,735
Advance royalties	31,641	32,241
Plant And Equipment	20,527	32,087
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	28,494	25,440
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities	19,327	21,798
Other	68,969	66,777
Gross Deferred Tax Assets	1,156,500	1,011,831
Valuation Allowance	-43,322	-34,663
Total Deferred Tax Assets	1,113,178	977,168
Deferred Tax Liabilities, Property, Plant and Equipment	1,364,382	1,411,446
Deferred Development	91,126	77,013
Investment in tax partnerships	8,170	72,513
Other	13,902	13,018
Tota Deferred Tax Liabilities	1,477,580	1,573,990
Net Deferred Tax Asset	$364,402	$596,822

Taxes_Schedule_of_Gross_Unreco

Taxes (Schedule of Gross Unrecognized Tax Benefits) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]	'	'	'
Beginning Balance	$31,150	$8,798	$4,418
Increases Resulting from Current Period Tax Positions	1,199	409	1,626
Increases Resulting from Prior Period Tax Positions	688	21,943	2,754
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	-1,248	'	'
Ending Balance	$31,789	$31,150	$8,798

Asset_Retirement_Obligations_N

Asset Retirement Obligations (Narrative) (Details) (USD $)	Dec. 31, 2012
In Millions, unless otherwise specified
asset retirement obligations [Line Items]	'
Letters of Credit Outstanding, Amount	$18.10
Asset retirement obligations [Member]	'
asset retirement obligations [Line Items]	'
Self-bonding obligations	417.6
Asset retirement obligations [Member]	'
asset retirement obligations [Line Items]	'
Surety bonds outstanding	$247.30

Asset_Retirement_Obligations_S

Asset Retirement Obligations (Schedule of Asset Retirement Obligations) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'	'
Beginning Balance	$448,625	$473,903
Accretion expense	35,727	39,020
Obligations incurred or acquired	-8,440	0
Adjustments to the liability from changes in estimates	-26,578	4,400
Liabilities settled	-21,681	-68,698
Ending Balance	427,653	448,625
Current portion included in accrued expenses	-24,940	-38,920
Noncurrent liability	$402,713	$409,705

Fair_Value_Measurements_Narrat

Fair Value Measurements (Narrative) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013
			Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'	'
Net unrealized losses related to level 3 financial instruments	'	'	$2,500,000
Fair value of senior notes and other long-term debt, including amounts classified as current	$4,600,000,000	$5,000,000,000	'

Fair_Value_Measurements_Summar

Fair Value Measurements (Summary of Financial Assets and Liabilities Accounted for at Fair Value) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Assets:	'	'
Investments in marketable securities	$264,443	$239,652
Derivatives	19,954	32,315
Total assets	284,397	'
Liabilities:	'	'
Coal derivative liabilities	12	1,737
Level 1 [Member]	'	'
Assets:	'	'
Investments in marketable securities	77,967	'
Derivatives	14,847	'
Total assets	92,814	'
Liabilities:	'	'
Coal derivative liabilities	'	'
Level 2 [Member]	'	'
Assets:	'	'
Investments in marketable securities	186,476	'
Derivatives	'	'
Total assets	186,476	'
Liabilities:	'	'
Coal derivative liabilities	-149	'
Level 3 [Member]	'	'
Assets:	'	'
Investments in marketable securities	'	'
Derivatives	5,107	'
Total assets	5,107	'
Liabilities:	'	'
Coal derivative liabilities	$161	'

Fair_Value_Measurements_Summar1

Fair Value Measurements (Summary of Change in the Fair Values of Financial Instruments Categorized as Level 3) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Balance, beginning of period	$8,174	$6,211
Realized and unrealized losses recognized in earnings, net	-10,253	-13,399
Purchases	8,654	0
Issuances	-25	17,312
Settlements	-1,604	-1,950
Ending balance	$4,946	$8,174

Capital_Stock_Narrative_Detail

Capital Stock (Narrative) (Details) (USD $)	0 Months Ended	5 Months Ended	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Jul. 12, 2011	Jun. 08, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Stock transactions	'	'	'	'	'
Common stock issued	'	'	'	'	48,705,000
Proceeds from the issuance of common stock, net	$18,400	$1,250,000	'	$0	$1,267,933
Stock repurchase authorized number	'	'	14,000,000	'	'
Outstanding shares available for repurchase	'	'	10,925,800	'	'
ICG [Member]	'	'	'	'	'
Stock transactions	'	'	'	'	'
Common stock issued	'	48,000,000	'	'	700,000
Common stock public offering price	'	$27	'	'	'

StockBased_Compensation_and_Ot2

Stock-Based Compensation and Other Incentive Plans (Narrative) (Details) (USD $)	12 Months Ended						3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2013
				long term incentive plan [Member]	long term incentive plan [Member]	long term incentive plan [Member]	Minimum [Member]	Maximum [Member]
							Employee Stock Option [Member]	Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Award Requisite Service Period	'	'	'	'3 years	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	10,300,000	'	'	'	'	'	'	'
Exercised, aggregate intrinsic value	'	$1,800,000	$2,600,000	'	'	'	'	'
Stock options compensation expense	6,700,000	8,000,000	8,800,000	'	'	'	'	'
Unrecognized compensation cost	4,900,000	'	'	'	'	'	'	'
Options vested in period fair value	8,900,000	8,000,000	9,900,000	'	'	'	'	'
Compensation expense	'	'	'	9,100,000	8,100,000	2,700,000	'	'
Amounts unpaid under long term incentive plan	17,200,000	13,100,000	'	'	'	'	'	'
Net cash surrender values	39,400,000	35,400,000	'	'	'	'	'	'
Participants maximum deferred amount in base salaries percentage	85.00%	'	'	'	'	'	'	'
Participants maximum deferred amount in annual incentive awards percentage	100.00%	'	'	'	'	'	'	'
Participants maximum deferred stock awards percentage	100.00%	'	'	'	'	'	'	'
Deferred compensation plan liability	37,000,000	31,300,000	'	'	'	'	'	'
Net income (expense) related to deferred compensation plan	2,600,000	3,300,000	6,200,000	'	'	'	'	'
Granted, Common Shares	1,998,000	'	'	'	'	'	'	'
Weighted average exercise price of options granted	$5.23	'	'	'	'	'	'	'
Weighted average grant-date fair value per share of options granted	$2.37	$5.27	$14.18	'	'	'	'	'
Option, weighted average risk free rate	0.65%	0.76%	1.92%	'	'	'	'	'
Option, weighted average dividend yield	2.30%	2.92%	1.25%	'	'	'	'	'
Option, weighted average volatility	66.70%	60.72%	57.40%	'	'	'	'	'
Expected life of options (Years)	'4 years 6 months	'4 years 6 months	'4 years 6 months	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	'	'	'	'	'	'	'3 years	'4 years
Shares authorized for incentive plan	30,900,000	'	'	'	'	'	'	'
Long term incentive plan amounts accrued	$67,621,000	$72,405,000	'	'	'	'	'	'

StockBased_Compensation_and_Ot3

Stock-Based Compensation and Other Incentive Plans (Schedule of Stock Option Activity Under Incentive Plan) (Details) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]	'	'	'
Options outstanding at January 1	5,215,000	'	'
Granted, Common Shares	1,998,000	'	'
Exercised, Common Shares	6,000	-526,000	-199,000
Cancelled, Common Shares	-138,000	'	'
Expired, Common Shares	-136,000	'	'
Options outstanding at December 31	6,939,000	5,215,000	'
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	7,500,000	4,900,000	2,600,000
Options exercisable at December 31	3,724,000	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$25.89	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$5.23	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price	$29.01	'	'
Share-based Compensation Arrangements by Share-based Payment Award, Options, Expirations in Period, Weighted Average Exercise Price	$31.57	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$19.86	$25.89	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price	$28.14	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$3	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value	$0	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	'6 years 8 months 12 days	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	'5 years 3 months 18 days	'	'

Stock_Based_Compensation_and_O

Stock Based Compensation and Other Incentive Plans (Changes in Stock Options Outstanding and not Yet Vested and Related Grant-Date Fair Value Under the Incentive Plan) (Details)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]	'	'	'
Options outstanding at January 1	2,369	3,216	'
Granted, Common Shares	1,998	'	'
Vested, Common Shares	-1,098	'	'
Cancelled, Common Shares	-53	'	'
Options outstanding at December 31	6,939	'	5,215
Unvested options, Weighted Average Grant-Date Fair Value	4.38	'	'
Granted, Weighted Average Grant-Date Fair Value	2.37	'	'
Vested, Weighted Average Grant-Date Fair Value	8.11	'	'
Canceled, Weighted Average Grant-Date Fair Value	3.97	'	'
Unvested options, Weighted Average Grant-Date Fair Value	7.72	'	'

StockBased_Compensation_and_Ot4

Stock-Based Compensation and Other Incentive Plans (Schedule of Weighted Average Assumptions Used in Option Pricing) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation [Abstract]	'	'	'
Weighted average grant-date fair value per share of options granted	$2.37	$5.27	$14.18
Option, weighted average risk free rate	0.65%	0.76%	1.92%
Option, weighted average dividend yield	2.30%	2.92%	1.25%
Option, weighted average volatility	66.70%	60.72%	57.40%
Expected life of options (Years)	'4 years 6 months	'4 years 6 months	'4 years 6 months

StockBased_Compensation_and_Ot5

Stock-Based Compensation and Other Incentive Plans (Restricted Stock and Restricted Stock Unit Activity and Weighted Average Grant-Date Fair Value) (Details) (USD $)	12 Months Ended			3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013
		Restricted Stock [Member]	Restricted Stock Units (RSUs) [Member]	Restricted Stock Units (RSUs) [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	'	'	'	'3 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]	'	'	'	'
Oustanding as of January 1	'	188	511	'
Shares granted during period	'	0	969	'
Vested	'	-44	-39	'
Canceled	'	0	-19	'
Outstanding as of December 31	'	144	1,422	'
Outstanding Weighted Average Grant Date Price	'	$27.55	$7.96	'
Weighted average fair value of restricted stock granted	'	'	$5.20	'
Vested, Weighted Average Grant-Date Fair Value	'	$17.30	$9.19	'
Canceled, Weighted Average Grant-Date Fair Value	3.97	0	7.21	'
Outstanding Weighted Average Grant Date Price	'	$25.14	$13.26	'

Workers_Compensation_Expense_W

Workers' Compensation Expense (Worker's Compensation Expense) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Workers' Compensation [Member]	'	'	'
Accrued Workers' Compensation [Line Items]	'	'	'
Total net benefit	$6,137,000	$6,962,000	$3,365,000
Traumatic injury claims and assessments	21,089,000	26,565,000	16,979,000
Total workers’ compensation expense	27,226,000	33,527,000	20,344,000
Workers' Compensation Benefits [Domain]	'	'	'
Accrued Workers' Compensation [Line Items]	'	'	'
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	900,000	'	'
Defined Benefit Plan, Curtailments	800,000	7,100,000	'
Surety Bonds And Letters Of Credit Outstanding	$98,800,000	'	'

Workers_Compensation_Expense_N

Workers' Compensation Expense (Narrative) (Details) (Workers' Compensation Benefits [Domain], USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Workers' Compensation Benefits [Domain]	'	'
Workers' Compensation [Line Items]	'	'
Defined Benefit Plan, Curtailments	$800,000	$7,100,000
Surety Bonds And Letters Of Credit Outstanding	98,800,000	'
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	$900,000	'

Workers_Compensation_Expense_S

Workers' Compensation Expense (Schedule of Amounts Recognized in Balance Sheet) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Accrued Workers' Compensation [Line Items]	'	'
Total obligations	$90,496	$92,000
Less amount included in accrued expenses	12,434	10,371
Noncurrent obligations	78,062	81,629
Occupational Disease [Member]	'	'
Accrued Workers' Compensation [Line Items]	'	'
Occupational disease costs	55,228	58,431
Workers' Compensation [Member]	'	'
Accrued Workers' Compensation [Line Items]	'	'
Occupational disease costs	$35,268	$33,569

Employee_Benefit_Plans_Narrati

Employee Benefit Plans (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Accumulated benefit obligation of pension plans	$341,100,000	$366,100,000	'
Benefit obligation for the unfunded pension plan	10,100,000	'	'
Accumulated benefit obligation for the unfunded pension plan	8,800,000	'	'
Health care cost trend rate assumed	7.30%	'	'
Ultimate trend rate	4.50%	'	'
Effect of one-percentage-point increase in health care cost trend rate	600,000	'	'
Effect of one-percentage-point decrease in health care cost trend rate	600,000	'	'
Level 3 [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Amount invested by plan	16,000,000	'	'
Equity Securities [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Defined Benefit Plan, Target Plan Asset Allocations	65.00%	'	'
Fixed Income Securities [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Defined Benefit Plan, Target Plan Asset Allocations	35.00%	'	'
Pension Plans, Defined Benefit [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Amortization of net prior service cost	200,000	'	'
Defined Benefit Plan, Amortization of Net Gains (Losses)	-3,800,000	'	'
Pension Contributions	4,000,000	'	'
Defined Benefit Plan, Plan Amendments	'	0	'
Pension Plans, Defined Benefit [Member] | Level 3 [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax	1,000,000	'	'
Defined Contribution Pension [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Other postretirement benefits payments	25,100,000	27,200,000	25,900,000
Other Postretirement Benefit Plans, Defined Benefit [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Amortization of net prior service cost	10,000,000	'	'
Defined Benefit Plan, Amortization of Net Gains (Losses)	700,000	'	'
Defined Benefit Plan, Plan Amendments	$0	$2,183,000	'

Employee_Benefit_Plans_Schedul

Employee Benefit Plans (Schedule of Defined Benefit Plans Disclosures) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Value of Plan Assets at December 31	'	$322,874	'
Pension Plans, Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'	'	'
Benefit Obligations at January 1	390,894	333,951	'
Service cost	27,065	27,466	16,490
Interest cost	16,207	15,668	16,253
Plan Amendments	'	0	'
Benefits Paid	-41,562	-23,624	'
Curtailments	-3,027	-687	'
Other-primary actuarial loss (gain)	-34,109	38,120	'
Benefit Obligations at December 31	355,468	390,894	333,951
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Value of Plan Assets at January 1	322,874	285,074	'
Actual Return on Plan Assets	52,247	42,396	'
Employer contributions	14,393	19,028	'
Benefits Paid	-41,562	-23,624	'
Value of Plan Assets at December 31	347,952	322,874	285,074
Accrued benefit cost	-7,516	-68,020	'
Prior service cost (credit)	1,732	1,890	'
Accumulated gain (loss)	10,096	-68,915	'
Total not yet recognized as a component of net periodic benefit cost	11,828	-67,025	'
Current liability	-405	-390	'
Noncurrent liability	-7,111	-67,630	'
Pension and Other Postretirement Defined Benefit Plans, Liabilities	-7,516	-68,020	'
Other Postretirement Benefit Plans, Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'	'	'
Benefit Obligations at January 1	49,326	45,129	'
Service cost	2,027	2,142	3,917
Interest cost	1,739	2,020	3,279
Plan Amendments	0	2,183	'
Benefits Paid	-3,276	-4,244	'
Curtailments	-2,519	-708	'
Other-primary actuarial loss (gain)	-4,766	2,804	'
Benefit Obligations at December 31	42,531	49,326	45,129
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Value of Plan Assets at January 1	0	0	'
Actual Return on Plan Assets	0	0	'
Employer contributions	3,276	4,244	'
Benefits Paid	-3,276	-4,244	'
Value of Plan Assets at December 31	0	0	0
Accrued benefit cost	-42,531	-49,326	'
Prior service cost (credit)	31,925	45,938	'
Accumulated gain (loss)	3,394	-1,531	'
Total not yet recognized as a component of net periodic benefit cost	35,319	44,407	'
Current liability	-3,276	-4,240	'
Noncurrent liability	-39,255	-45,086	'
Pension and Other Postretirement Defined Benefit Plans, Liabilities	($42,531)	($49,326)	'

Employee_Benefit_Plans_Schedul1

Employee Benefit Plans (Schedule of Net Benefit Costs) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Plans, Defined Benefit [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Service cost	$27,065	$27,466	$16,490
Interest cost	16,207	15,668	16,253
Curtailments	47	324	0
Expected return on plan assets	-23,761	-22,030	-21,812
Amortization of prior service cost (credit)	-204	259	-189
Amortization of other actuarial (gains) losses	14,616	14,666	8,748
Total net benefit	33,970	36,353	19,490
Other Postretirement Benefit Plans, Defined Benefit [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Service cost	2,027	2,142	3,917
Interest cost	1,739	2,020	3,279
Curtailments	-5,444	-4,049	0
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	-10,621	-11,458	-2,364
Amortization of other actuarial (gains) losses	-252	-522	-3,100
Total net benefit	($12,551)	($11,867)	$1,732

Employee_Benefit_Plans_Schedul2

Employee Benefit Plans (Schedule of Assumptions Used to Calculate Benefit Obligations) (Details)	Dec. 31, 2013	Dec. 31, 2012
Pension Plans, Defined Benefit [Member]	'	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'	'
Discount rate	5.08%	4.13%
Rate of compensation increase	3.39%	3.39%
Other Postretirement Benefit Plans, Defined Benefit [Member]	'	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'	'
Discount rate	4.58%	3.64%

Employee_Benefit_Plans_Schedul3

Employee Benefit Plans (Schedule of Assumptions Used) (Details)	4 Months Ended	8 Months Ended	12 Months Ended
	Dec. 31, 2013	Aug. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Plans, Defined Benefit [Member]	'	'	'	'	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'	'	'	'	'
Discount Rate	5.05%	4.13%	'	4.91%	5.71%
Rate of Compensation Increase	'	'	3.39%	3.39%	3.39%
Expected return on plan assets	'	'	7.75%	7.75%	8.50%
Other Postretirement Benefit Plans, Defined Benefit [Member]	'	'	'	'	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'	'	'	'	'
Discount Rate	4.58%	3.64%	'	4.52%	5.23%

Employee_Benefit_Plans_Schedul4

Employee Benefit Plans (Schedule of Allocation of Plan Assets) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	'	$322,874
Fair Value, Inputs, Level 1 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	114,977	97,835
Fair Value, Inputs, Level 2 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	215,958	225,039
Level 3 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	17,017	'
U.S. Small-Cap [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	14,901	13,099
U.S. Small-Cap [Member] | Fair Value, Inputs, Level 1 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	14,901	13,099
U.S. Small-Cap [Member] | Fair Value, Inputs, Level 2 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	'	'
U.S. Mid-Cap [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	62,271	43,946
U.S. Mid-Cap [Member] | Fair Value, Inputs, Level 1 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	28,654	12,717
U.S. Mid-Cap [Member] | Fair Value, Inputs, Level 2 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	33,617	31,229
U.S. Large-Cap [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	110,947	102,922
U.S. Large-Cap [Member] | Fair Value, Inputs, Level 1 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	53,708	48,536
U.S. Large-Cap [Member] | Fair Value, Inputs, Level 2 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	57,239	54,386
Non-U.S. [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	29,165	27,251
Non-U.S. [Member] | Fair Value, Inputs, Level 1 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	'	'
Non-U.S. [Member] | Fair Value, Inputs, Level 2 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	29,165	27,251
U.S. Government Securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	18,545	24,202
U.S. Government Securities [Member] | Fair Value, Inputs, Level 1 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	17,714	23,483
U.S. Government Securities [Member] | Fair Value, Inputs, Level 2 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	831	719
Non-U.S. Government Securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	2,143	3,681
Non-U.S. Government Securities [Member] | Fair Value, Inputs, Level 1 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	'	'
Non-U.S. Government Securities [Member] | Fair Value, Inputs, Level 2 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	2,143	3,681
U.S. governement asset and mortgage backed securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	600	781
U.S. governement asset and mortgage backed securities [Member] | Fair Value, Inputs, Level 1 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	'	'
U.S. governement asset and mortgage backed securities [Member] | Fair Value, Inputs, Level 2 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	600	781
Corporate fixed income [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	9,902	14,016
Corporate fixed income [Member] | Fair Value, Inputs, Level 1 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	'	'
Corporate fixed income [Member] | Fair Value, Inputs, Level 2 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	9,902	14,016
State and Local Government Securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	8,301	9,903
State and Local Government Securities [Member] | Fair Value, Inputs, Level 1 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	'	'
State and Local Government Securities [Member] | Fair Value, Inputs, Level 2 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	8,301	9,903
Other fixed income [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	58,093	61,765
Other fixed income [Member] | Fair Value, Inputs, Level 1 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	'	'
Other fixed income [Member] | Fair Value, Inputs, Level 2 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	58,093	61,765
Short-term Investments [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	14,663	20,894
Short-term Investments [Member] | Fair Value, Inputs, Level 1 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	'	'
Short-term Investments [Member] | Fair Value, Inputs, Level 2 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	14,663	20,894
Other Investments [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	18,421	414
Other Investments [Member] | Fair Value, Inputs, Level 1 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	'	'
Other Investments [Member] | Fair Value, Inputs, Level 2 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	1,404	414
Other Investments [Member] | Level 3 [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Fair Value of Plan Assets	$17,017	'

Employee_Benefit_Plans_Summary

Employee Benefit Plans (Summary of Estimated Future Benefit Payments) (Details) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Pension Plans, Defined Benefit [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	$21,844
Defined Benefit Plan, Expected Future Benefit Payments, Rolling Year Two	21,666
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	27,689
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	29,999
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	33,488
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	190,030
DefinedBenefitPlanExpectedFutureBenefitPaymentsTotal	324,716
Other Postretirement Benefit Plans, Defined Benefit [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	4,020
Defined Benefit Plan, Expected Future Benefit Payments, Rolling Year Two	4,226
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	4,415
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	4,523
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	4,602
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	22,028
DefinedBenefitPlanExpectedFutureBenefitPaymentsTotal	$43,814

Earnings_Loss_Per_Common_Share1

Earnings (Loss) Per Common Share (Narrative) (Details)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share [Abstract]	'	'	'
Earnings Per Share, Potentially Dilutive Securities	'	'	'819
Effect of options to purchase common stock	7.5	4.9	2.6

Leases_Narrative_Details

Leases (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
lease payments [Line Items]	'	'	'
Rental expense	$42.20	$41.20	$43.90
Royalty expense	261.1	302	349
lease [Member]	'	'	'
lease payments [Line Items]	'	'	'
Surety bonds outstanding	$55.40	'	'

Leases_Schedule_of_Lease_Minim

Leases (Schedule of Lease Minimum Payments) (Details) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Property Subject to Operating Lease [Member]	'
lease payments [Line Items]	'
Operating Leases, Future Minimum Payments Due, Next Twelve Months	$31,532
Operating Leases, Future Minimum Payments, Due in Two Years	24,466
Operating Leases, Future Minimum Payments, Due in Three Years	16,851
Operating Leases, Future Minimum Payments, Due in Four Years	14,509
Operating Leases, Future Minimum Payments, Due in Five Years	3,739
Operating Leases, Future Minimum Payments, Due Thereafter	1,195
Operating Leases, Future Minimum Payments Due	92,292
Royalty Agreements [Member]	'
lease payments [Line Items]	'
Operating Leases, Future Minimum Payments Due, Next Twelve Months	17,394
Operating Leases, Future Minimum Payments, Due in Two Years	19,143
Operating Leases, Future Minimum Payments, Due in Three Years	21,070
Operating Leases, Future Minimum Payments, Due in Four Years	20,806
Operating Leases, Future Minimum Payments, Due in Five Years	22,255
Operating Leases, Future Minimum Payments, Due Thereafter	83,708
Operating Leases, Future Minimum Payments Due	$184,376

Risk_Concentrations_Narrative_

Risk Concentrations (Narrative) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
	T
Concentration Risk [Line Items]	'	'	'
Sales to customers in foreign countries	$800,000	$1,153,100	$900,000
Receivables	229,573	332,080	'
Trade accounts receivable	198,020	247,539	'
Tons of coal sold	139,600,000	'	'
Percentage of tons sold under long term contract	59.00%	'	'
Long term contracts percentage of company revenue	49.00%	'	'
Long-term contracts, life term, minimum	'1 year	'	'
Long-term contracts, life term, maximum	'7 years	'	'
Electric Utilities [Member]	'	'	'
Concentration Risk [Line Items]	'	'	'
Receivables	125,700	159,500	'
Percentage of total trade accounts receivable	64.00%	65.00%	'
Domestic And Foreign Steel Producers [Member]	'	'	'
Concentration Risk [Line Items]	'	'	'
Trade accounts receivable	$70,500	$86,600	'
Trade receivables, percentage	36.00%	35.00%	'

Risk_Concentrations_Schedule_o

Risk Concentrations (Schedule of Foreign Revenues) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
foreign revenue [Line Items]	'	'	'
Sales to customers in foreign countries	$800,000	$1,153,100	$900,000
Europe [Member]	'	'	'
foreign revenue [Line Items]	'	'	'
Sales to customers in foreign countries	371,363	'	'
Asia [Member]	'	'	'
foreign revenue [Line Items]	'	'	'
Sales to customers in foreign countries	160,404	'	'
North America [Member]	'	'	'
foreign revenue [Line Items]	'	'	'
Sales to customers in foreign countries	80,322	'	'
South America [Member]	'	'	'
foreign revenue [Line Items]	'	'	'
Sales to customers in foreign countries	55,493	'	'
Brokered Sales [Member]	'	'	'
foreign revenue [Line Items]	'	'	'
Sales to customers in foreign countries	154,442	'	'
Total [Member]	'	'	'
foreign revenue [Line Items]	'	'	'
Sales to customers in foreign countries	$822,024	'	'

Settlement_with_Patriot_Coal_D

Settlement with Patriot Coal (Details) (USD $)	1 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Jul. 31, 2013	Dec. 31, 2013
Settlement with Patriot Coal [Abstract]	'	'
Payments for Legal Settlements	$15.60	$5
Letters of credit posted in the Company's favor	'	16.7
Payments to Acquire Mineral Rights	'	$16

Commitments_and_Contingencies_

Commitments and Contingencies (Narrative) (Details) (USD $)	1 Months Ended	12 Months Ended					1 Months Ended
In Millions, unless otherwise specified	Jul. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Aug. 25, 2011	Aug. 13, 2007	Dec. 31, 2013	Feb. 01, 2011	Feb. 01, 2011	Aug. 25, 2011	Aug. 25, 2011
						Coal, materials and supplies and capital commitments, other than reserve acquisitions, and transportation capacity agreements [Member]	Minimum [Member]	Maximum [Member]	past damages [Member]	future damages [Member]
Loss Contingencies [Line Items]	'	'	'	'	'	'	'	'	'	'
Purchase replacement coal	'	'	'	'	$100	'	'	'	'	'
Aggregate amount of past and future damages	'	'	'	'	'	'	228	377	'	'
Damages and interest awarded	'	'	'	104.1	'	'	'	'	13.8	90.3
Payments for Legal Settlements	15.6	5	'	'	'	'	'	'	'	'
Amount accrued	'	30.4	32.8	'	'	'	'	'	'	'
Amount accrued current portion	'	11.7	4.4	'	'	'	'	'	'	'
Unrecorded Unconditional Purchase Obligation [Line Items]	'	'	'	'	'	'	'	'	'	'
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	'	'	'	'	'	293	'	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	'	'	'	'	'	145.8	'	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	'	'	'	'	'	111.3	'	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	'	'	'	'	'	105.7	'	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	'	'	'	'	'	80.8	'	'	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	'	$407.70	'	'	'	'	'	'	'	'

Segment_Information_Schedule_o

Segment Information (Schedule of Operating Segment Results) (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenues	$719,386	$791,269	$766,332	$737,370	$867,034	$975,170	$965,685	$960,237	$3,014,357	$3,768,126	$3,883,039
Income (loss) from operations	'	-234,753	-36,279	-51,431	-307,158	119,242	-596,893	27,797	-663,141	-757,012	343,061
Depreciation, depletion and amortization	'	'	'	'	'	'	'	'	426,442	492,211	420,980
Depreciation, depletion and amortization	'	'	'	'	'	'	'	'	447,704	525,508	466,587
Amortization of acquired sales contracts, net	'	'	'	'	'	'	'	'	-9,457	-25,189	-22,069
Sales contract amortization	'	'	'	'	'	'	'	'	-9,457	-25,189	-22,069
Total assets	8,990,193	'	'	'	10,006,777	'	'	'	8,990,193	10,006,777	10,213,959
Capital expenditures	'	'	'	'	'	'	'	'	296,984	395,225	540,936
PRB [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenues	'	'	'	'	'	'	'	'	1,482,813	1,524,536	1,646,947
Income (loss) from operations	'	'	'	'	'	'	'	'	41,543	100,679	180,730
Depreciation, depletion and amortization	'	'	'	'	'	'	'	'	171,324	166,539	'
Depreciation, depletion and amortization	'	'	'	'	'	'	'	'	'	'	171,693
Sales contract amortization	'	'	'	'	'	'	'	'	-3,656	-1,987	19,458
Total assets	1,841,835	'	'	'	'	'	'	'	1,841,835	'	2,307,783
Capital expenditures	'	'	'	'	'	'	'	'	9,784	23,410	110,999
APP [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenues	'	'	'	'	'	'	'	'	1,145,800	1,793,576	1,915,090
Income (loss) from operations	'	'	'	'	'	'	'	'	-108,387	-606,235	283,404
Depreciation, depletion and amortization	'	'	'	'	'	'	'	'	202,952	271,220	'
Depreciation, depletion and amortization	'	'	'	'	'	'	'	'	'	'	203,759
Sales contract amortization	'	'	'	'	'	'	'	'	-10,364	-23,926	-39,988
Total assets	3,971,764	'	'	'	'	'	'	'	3,971,764	'	4,740,723
Capital expenditures	'	'	'	'	'	'	'	'	167,759	275,476	217,435
Other Segments [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenues	'	'	'	'	'	'	'	'	385,744	450,014	321,002
Income (loss) from operations	'	'	'	'	'	'	'	'	64,943	74,142	44,465
Depreciation, depletion and amortization	'	'	'	'	'	'	'	'	45,741	49,911	'
Depreciation, depletion and amortization	'	'	'	'	'	'	'	'	'	'	43,504
Sales contract amortization	'	'	'	'	'	'	'	'	4,563	724	-1,539
Total assets	402,922	'	'	'	834,287	'	'	'	402,922	834,287	1,262,433
Capital expenditures	'	'	'	'	'	'	'	'	23,122	68,220	94,599
Corporate, Other and Eliminations [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenues	'	'	'	'	'	'	'	'	'	'	'
Income (loss) from operations	'	'	'	'	'	'	'	'	-661,240	-325,598	-165,538
Depreciation, depletion and amortization	'	'	'	'	'	'	'	'	6,425	4,541	'
Depreciation, depletion and amortization	'	'	'	'	'	'	'	'	'	'	2,024
Sales contract amortization	'	'	'	'	'	'	'	'	'	'	'
Total assets	2,773,672	'	'	'	3,324,863	'	'	'	2,773,672	3,324,863	1,903,020
Capital expenditures	'	'	'	'	'	'	'	'	$96,319	$28,119	$117,903

Segment_Information_Reconcilia

Segment Information (Reconciliation of Segment Income from Operations to Consolidated Income Before Income Taxes) (Details) (USD $)	3 Months Ended							12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting [Abstract]	'	'	'	'	'	'	'	'	'	'
Income (loss) from operations	($234,753)	($36,279)	($51,431)	($307,158)	$119,242	($596,893)	$27,797	($663,141)	($757,012)	$343,061
Interest expense	'	'	'	'	'	'	'	-381,267	-317,615	-230,186
Interest and investment income	'	'	'	'	'	'	'	6,603	5,473	3,309
Nonoperating expense	'	'	'	'	'	'	'	-42,921	-23,668	-51,448
Loss from continuing operations before income taxes	'	'	'	'	'	'	'	($1,080,726)	($1,092,822)	$64,736

Quarterly_Financial_Informatio2

Quarterly Financial Information (Details) (USD $)	3 Months Ended								7 Months Ended	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Aug. 16, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information [Abstract]	'	'	'	'	'	'	'	'	'	'	'	'
Coal Products and Services Revenue	$719,386	$791,269	$766,332	$737,370	$867,034	$975,170	$965,685	$960,237	'	$3,014,357	$3,768,126	$3,883,039
Gross Profit	-44,801	90	2,505	-18,560	12,516	53,017	47,163	37,715	'	'	'	'
Asset impairment and mine closure costs	0	200,397	20,482	0	15,743	-2,144	525,583	0	'	220,879	539,182	7,316
Goodwill, Impairment Loss	'	0	0	0	'	0	115,791	0	'	265,423	330,680	0
Asset Impairment Charges	265,423	'	'	'	214,889	'	'	'	'	'	'	'
Income (loss) from operations	'	-234,753	-36,279	-51,431	-307,158	119,242	-596,893	27,797	'	-663,141	-757,012	343,061
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	-372,794	-207,767	-80,351	-84,316	-307,033	24,673	-442,456	-14,099	'	-745,228	-738,915	89,015
Income from discontinued operations, including gain on sale - net of tax	1,580	79,404	8,145	14,267	11,610	21,078	7,032	15,508	103,396	103,396	55,228	53,825
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	($371,214)	($128,363)	($72,206)	($70,049)	($295,423)	$45,751	($435,424)	$1,409	'	($641,832)	($683,687)	$142,840
Income (Loss) from Continuing Operations, Per Diluted Share	($1.76)	($0.98)	($0.38)	($0.40)	($1.45)	$0.12	($2.09)	($0.07)	'	($3.52)	($3.50)	$0.47
Earnings Per Share, Diluted	($1.75)	($0.61)	($0.34)	($0.33)	($1.39)	$0.22	($2.05)	$0.01	'	($3.03)	($3.24)	$0.74

Supplemental_Consolidating_Fin2

Supplemental Consolidating Financial Information (Schedule of Consolidating Statements of Operations) (Details) (USD $)

3 Months Ended

7 Months Ended

12 Months Ended

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Aug. 16, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Condensed Financial Statement Line Items

'

'

'

'

'

'

'

'

'

'

'

'

Revenues

$719,386,000

$791,269,000

$766,332,000

$737,370,000

$867,034,000

$975,170,000

$965,685,000

$960,237,000

'

$3,014,357,000

$3,768,126,000

$3,883,039,000

Costs, expenses and other

'

'

'

'

'

'

'

'

'

'

'

'

Cost of sales (exclusive of items shown separately below)

'

'

'

'

'

'

'

'

'

2,663,136,000

3,155,099,000

2,980,354,000

Depreciation, depletion and amortization

'

'

'

'

'

'

'

'

'

426,442,000

492,211,000

420,980,000

Amortization of acquired sales contracts, net

'

'

'

'

'

'

'

'

'

-9,457,000

-25,189,000

-22,069,000

Change in fair value of coal derivatives and coal trading activities, net

'

'

'

'

'

'

'

'

'

7,845,000

-16,590,000

-2,907,000

Asset impairment and mine closure costs

0

200,397,000

20,482,000

0

15,743,000

-2,144,000

525,583,000

0

'

220,879,000

539,182,000

7,316,000

Acquisition and transition costs

'

'

'

'

'

'

'

'

'

0

0

47,360,000

Goodwill impairment

'

0

0

0

'

0

115,791,000

0

'

265,423,000

330,680,000

0

Contract settlement resulting from Patriot Coal bankruptcy

'

'

'

'

'

'

'

'

'

0

58,335,000

0

Reduction in accrual related to acquired litigation

'

'

'

'

'

'

'

'

'

'

-79,532,000

0

Selling, general and administrative expenses

'

'

'

'

'

'

'

'

'

133,448,000

134,299,000

119,056,000

Other operating expense (income), net

'

'

'

'

'

'

'

'

'

2,316,000

-19,367,000

-10,119,000

Other Income

'

'

'

'

'

'

'

'

'

30,218,000

63,357,000

10,112,000

Total operating expenses

'

'

'

'

'

'

'

'

'

3,677,498,000

4,525,138,000

3,539,978,000

Loss from investment in subsidiaries

'

'

'

'

'

'

'

'

'

'

'

'

Income (loss) from operations

'

-234,753,000

-36,279,000

-51,431,000

-307,158,000

119,242,000

-596,893,000

27,797,000

'

-663,141,000

-757,012,000

343,061,000

Interest expense, net

'

'

'

'

'

'

'

'

'

'

'

'

Interest expense

'

'

'

'

'

'

'

'

'

-381,267,000

-317,615,000

-230,186,000

Interest and investment income

'

'

'

'

'

'

'

'

'

6,603,000

5,473,000

3,309,000

Interest Income (Expense), Nonoperating, Net

'

'

'

'

'

'

'

'

'

-374,664,000

-312,142,000

-226,877,000

Other Nonoperating Income (Expense) [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

Net loss resulting from early retirement of debt and financing activities

'

'

'

'

'

'

'

'

'

-42,921,000

-23,668,000

-51,448,000

Net loss resulting from early retirement and refinancing of debt

'

'

'

'

'

'

'

'

'

-42,921,000

-23,668,000

-1,958,000

Loss from continuing operations before income taxes

'

'

'

'

'

'

'

'

'

-1,080,726,000

-1,092,822,000

64,736,000

Provision for (benefit from) income taxes

'

'

'

'

'

'

'

'

'

-335,498,000

-353,907,000

-24,279,000

Income (loss) from continuing operations

-372,794,000

-207,767,000

-80,351,000

-84,316,000

-307,033,000

24,673,000

-442,456,000

-14,099,000

'

-745,228,000

-738,915,000

89,015,000

Income from discontinued operations, including gain on sale - net of tax

1,580,000

79,404,000

8,145,000

14,267,000

11,610,000

21,078,000

7,032,000

15,508,000

103,396,000

103,396,000

55,228,000

53,825,000

Net income (loss)

-371,214,000

-128,363,000

-72,206,000

-70,049,000

-295,423,000

45,751,000

-435,424,000

1,409,000

'

-641,832,000

-683,687,000

142,840,000

Less: Net income attributable to noncontrolling interest

'

'

'

'

'

'

'

'

'

'

-268,000

-1,157,000

Net income (loss) attributable to Arch Coal, Inc.

'

'

'

'

'

'

'

'

'

-641,832,000

-683,955,000

141,683,000

Total comprehensive income (loss)

'

'

'

'

'

'

'

'

'

-587,633,000

-692,239,000

141,240,000

Parent/Issuer [Member]

'

'

'

'

'

'

'

'

'

'

'

'

Condensed Financial Statement Line Items

'

'

'

'

'

'

'

'

'

'

'

'

Revenues

'

'

'

'

'

'

'

'

'

'

'

'

Costs, expenses and other

'

'

'

'

'

'

'

'

'

'

'

'

Cost of sales (exclusive of items shown separately below)

'

'

'

'

'

'

'

'

'

9,117,000

10,921,000

22,929,000

Depreciation, depletion and amortization

'

'

'

'

'

'

'

'

'

5,949,000

5,392,000

2,876,000

Amortization of acquired sales contracts, net

'

'

'

'

'

'

'

'

'

'

'

'

Change in fair value of coal derivatives and coal trading activities, net

'

'

'

'

'

'

'

'

'

'

'

'

Asset impairment and mine closure costs

'

'

'

'

'

'

'

'

'

78,150,000

'

'

Acquisition and transition costs

'

'

'

'

'

'

'

'

'

'

'

47,360,000

Goodwill impairment

'

'

'

'

'

'

'

'

'

0

'

'

Contract settlement resulting from Patriot Coal bankruptcy

'

'

'

'

'

'

'

'

'

'

'

'

Reduction in accrual related to acquired litigation

'

'

'

'

'

'

'

'

'

'

'

'

Selling, general and administrative expenses

'

'

'

'

'

'

'

'

'

88,820,000

84,199,000

74,591,000

Other operating expense (income), net

'

'

'

'

'

'

'

'

'

4,209,000

-13,392,000

-23,306,000

Total operating expenses

'

'

'

'

'

'

'

'

'

186,245,000

87,120,000

124,450,000

Loss from investment in subsidiaries

'

'

'

'

'

'

'

'

'

-328,889,000

-589,665,000

532,757,000

Income (loss) from operations

'

'

'

'

'

'

'

'

'

-515,134,000

-676,785,000

408,307,000

Interest expense, net

'

'

'

'

'

'

'

'

'

'

'

'

Interest expense

'

'

'

'

'

'

'

'

'

-449,614,000

-366,584,000

-256,191,000

Interest and investment income

'

'

'

'

'

'

'

'

'

30,285,000

27,750,000

15,935,000

Interest Income (Expense), Nonoperating, Net

'

'

'

'

'

'

'

'

'

-419,329,000

-338,834,000

-240,256,000

Other Nonoperating Income (Expense) [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

Net loss resulting from early retirement of debt and financing activities

'

'

'

'

'

'

'

'

'

'

'

-49,490,000

Net loss resulting from early retirement and refinancing of debt

'

'

'

'

'

'

'

'

'

-42,921,000

-21,975,000

'

Loss from continuing operations before income taxes

'

'

'

'

'

'

'

'

'

-977,384,000

-1,037,594,000

118,561,000

Provision for (benefit from) income taxes

'

'

'

'

'

'

'

'

'

-335,552,000

-353,907,000

-24,279,000

Income (loss) from continuing operations

'

'

'

'

'

'

'

'

'

-641,832,000

-683,687,000

142,840,000

Income from discontinued operations, including gain on sale - net of tax

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss)

'

'

'

'

'

'

'

'

'

'

-683,687,000

142,840,000

Less: Net income attributable to noncontrolling interest

'

'

'

'

'

'

'

'

'

'

-268,000

-1,157,000

Net income (loss) attributable to Arch Coal, Inc.

'

'

'

'

'

'

'

'

'

-641,832,000

-683,955,000

141,683,000

Total comprehensive income (loss)

'

'

'

'

'

'

'

'

'

-587,633,000

-692,239,000

141,240,000

Guarantor Subsidiaries [Member]

'

'

'

'

'

'

'

'

'

'

'

'

Condensed Financial Statement Line Items

'

'

'

'

'

'

'

'

'

'

'

'

Revenues

'

'

'

'

'

'

'

'

'

3,014,357,000

3,768,126,000

3,883,039,000

Costs, expenses and other

'

'

'

'

'

'

'

'

'

'

'

'

Cost of sales (exclusive of items shown separately below)

'

'

'

'

'

'

'

'

'

2,657,583,000

3,144,178,000

2,957,425,000

Depreciation, depletion and amortization

'

'

'

'

'

'

'

'

'

420,458,000

486,786,000

418,104,000

Amortization of acquired sales contracts, net

'

'

'

'

'

'

'

'

'

-9,457,000

-25,189,000

-22,069,000

Change in fair value of coal derivatives and coal trading activities, net

'

'

'

'

'

'

'

'

'

7,845,000

-16,590,000

-2,907,000

Asset impairment and mine closure costs

'

'

'

'

'

'

'

'

'

142,729,000

539,182,000

7,316,000

Acquisition and transition costs

'

'

'

'

'

'

'

'

'

'

'

0

Goodwill impairment

'

'

'

'

'

'

'

'

'

265,423,000

330,680,000

'

Contract settlement resulting from Patriot Coal bankruptcy

'

'

'

'

'

'

'

'

'

'

58,335,000

'

Reduction in accrual related to acquired litigation

'

'

'

'

'

'

'

'

'

'

-79,532,000

'

Selling, general and administrative expenses

'

'

'

'

'

'

'

'

'

39,825,000

44,363,000

43,572,000

Other operating expense (income), net

'

'

'

'

'

'

'

'

'

-34,856,000

-39,209,000

10,811,000

Total operating expenses

'

'

'

'

'

'

'

'

'

3,489,550,000

4,443,004,000

3,412,252,000

Loss from investment in subsidiaries

'

'

'

'

'

'

'

'

'

'

'

'

Income (loss) from operations

'

'

'

'

'

'

'

'

'

-475,193,000

-674,878,000

470,787,000

Interest expense, net

'

'

'

'

'

'

'

'

'

'

'

'

Interest expense

'

'

'

'

'

'

'

'

'

-24,747,000

-34,849,000

-46,218,000

Interest and investment income

'

'

'

'

'

'

'

'

'

68,248,000

57,268,000

55,041,000

Interest Income (Expense), Nonoperating, Net

'

'

'

'

'

'

'

'

'

43,501,000

22,419,000

8,823,000

Other Nonoperating Income (Expense) [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

Net loss resulting from early retirement of debt and financing activities

'

'

'

'

'

'

'

'

'

'

'

-1,958,000

Net loss resulting from early retirement and refinancing of debt

'

'

'

'

'

'

'

'

'

0

-1,693,000

'

Loss from continuing operations before income taxes

'

'

'

'

'

'

'

'

'

-431,692,000

-654,152,000

477,652,000

Provision for (benefit from) income taxes

'

'

'

'

'

'

'

'

'

'

'

'

Income (loss) from continuing operations

'

'

'

'

'

'

'

'

'

-431,692,000

-654,152,000

477,652,000

Income from discontinued operations, including gain on sale - net of tax

'

'

'

'

'

'

'

'

'

103,396,000

55,228,000

53,825,000

Net income (loss)

'

'

'

'

'

'

'

'

'

'

-598,924,000

531,477,000

Less: Net income attributable to noncontrolling interest

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss) attributable to Arch Coal, Inc.

'

'

'

'

'

'

'

'

'

-328,296,000

-598,924,000

531,477,000

Total comprehensive income (loss)

'

'

'

'

'

'

'

'

'

-304,278,000

-604,903,000

537,561,000

Non-Guarantor Subsidiaries [Member]

'

'

'

'

'

'

'

'

'

'

'

'

Condensed Financial Statement Line Items

'

'

'

'

'

'

'

'

'

'

'

'

Revenues

'

'

'

'

'

'

'

'

'

'

'

'

Costs, expenses and other

'

'

'

'

'

'

'

'

'

'

'

'

Cost of sales (exclusive of items shown separately below)

'

'

'

'

'

'

'

'

'

'

'

'

Depreciation, depletion and amortization

'

'

'

'

'

'

'

'

'

35,000

33,000

0

Amortization of acquired sales contracts, net

'

'

'

'

'

'

'

'

'

'

'

'

Change in fair value of coal derivatives and coal trading activities, net

'

'

'

'

'

'

'

'

'

'

'

'

Asset impairment and mine closure costs

'

'

'

'

'

'

'

'

'

'

'

'

Acquisition and transition costs

'

'

'

'

'

'

'

'

'

'

'

0

Goodwill impairment

'

'

'

'

'

'

'

'

'

0

'

'

Contract settlement resulting from Patriot Coal bankruptcy

'

'

'

'

'

'

'

'

'

'

'

'

Reduction in accrual related to acquired litigation

'

'

'

'

'

'

'

'

'

'

'

'

Selling, general and administrative expenses

'

'

'

'

'

'

'

'

'

7,038,000

8,785,000

3,527,000

Other operating expense (income), net

'

'

'

'

'

'

'

'

'

-5,370,000

-13,804,000

-251,000

Total operating expenses

'

'

'

'

'

'

'

'

'

1,703,000

-4,986,000

3,276,000

Loss from investment in subsidiaries

'

'

'

'

'

'

'

'

'

'

'

'

Income (loss) from operations

'

'

'

'

'

'

'

'

'

-1,703,000

4,986,000

-3,276,000

Interest expense, net

'

'

'

'

'

'

'

'

'

'

'

'

Interest expense

'

'

'

'

'

'

'

'

'

-4,214,000

-3,221,000

-2,224,000

Interest and investment income

'

'

'

'

'

'

'

'

'

5,378,000

7,494,000

6,780,000

Interest Income (Expense), Nonoperating, Net

'

'

'

'

'

'

'

'

'

1,164,000

4,273,000

4,556,000

Other Nonoperating Income (Expense) [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

Net loss resulting from early retirement of debt and financing activities

'

'

'

'

'

'

'

'

'

'

'

0

Net loss resulting from early retirement and refinancing of debt

'

'

'

'

'

'

'

'

'

0

'

'

Loss from continuing operations before income taxes

'

'

'

'

'

'

'

'

'

-539,000

9,259,000

1,280,000

Provision for (benefit from) income taxes

'

'

'

'

'

'

'

'

'

54,000

'

'

Income (loss) from continuing operations

'

'

'

'

'

'

'

'

'

-593,000

9,259,000

1,280,000

Income from discontinued operations, including gain on sale - net of tax

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss)

'

'

'

'

'

'

'

'

'

'

9,259,000

1,280,000

Less: Net income attributable to noncontrolling interest

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss) attributable to Arch Coal, Inc.

'

'

'

'

'

'

'

'

'

-593,000

9,259,000

1,280,000

Total comprehensive income (loss)

'

'

'

'

'

'

'

'

'

-593,000

9,259,000

1,280,000

Eliminations [Member]

'

'

'

'

'

'

'

'

'

'

'

'

Condensed Financial Statement Line Items

'

'

'

'

'

'

'

'

'

'

'

'

Revenues

'

'

'

'

'

'

'

'

'

'

'

'

Costs, expenses and other

'

'

'

'

'

'

'

'

'

'

'

'

Cost of sales (exclusive of items shown separately below)

'

'

'

'

'

'

'

'

'

-3,564,000

'

'

Depreciation, depletion and amortization

'

'

'

'

'

'

'

'

'

'

'

'

Amortization of acquired sales contracts, net

'

'

'

'

'

'

'

'

'

'

'

'

Change in fair value of coal derivatives and coal trading activities, net

'

'

'

'

'

'

'

'

'

'

'

'

Asset impairment and mine closure costs

'

'

'

'

'

'

'

'

'

'

'

'

Acquisition and transition costs

'

'

'

'

'

'

'

'

'

'

'

0

Goodwill impairment

'

'

'

'

'

'

'

'

'

0

'

'

Contract settlement resulting from Patriot Coal bankruptcy

'

'

'

'

'

'

'

'

'

'

'

'

Reduction in accrual related to acquired litigation

'

'

'

'

'

'

'

'

'

'

'

'

Selling, general and administrative expenses

'

'

'

'

'

'

'

'

'

-2,235,000

-3,048,000

-2,634,000

Other operating expense (income), net

'

'

'

'

'

'

'

'

'

5,799,000

3,048,000

2,634,000

Total operating expenses

'

'

'

'

'

'

'

'

'

'

'

'

Loss from investment in subsidiaries

'

'

'

'

'

'

'

'

'

328,889,000

589,665,000

-532,757,000

Income (loss) from operations

'

'

'

'

'

'

'

'

'

328,889,000

589,665,000

-532,757,000

Interest expense, net

'

'

'

'

'

'

'

'

'

'

'

'

Interest expense

'

'

'

'

'

'

'

'

'

97,308,000

87,039,000

74,447,000

Interest and investment income

'

'

'

'

'

'

'

'

'

-97,308,000

-87,039,000

-74,447,000

Interest Income (Expense), Nonoperating, Net

'

'

'

'

'

'

'

'

'

0

0

0

Other Nonoperating Income (Expense) [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

Net loss resulting from early retirement of debt and financing activities

'

'

'

'

'

'

'

'

'

'

'

0

Net loss resulting from early retirement and refinancing of debt

'

'

'

'

'

'

'

'

'

0

'

'

Loss from continuing operations before income taxes

'

'

'

'

'

'

'

'

'

328,889,000

589,665,000

-532,757,000

Provision for (benefit from) income taxes

'

'

'

'

'

'

'

'

'

'

'

'

Income (loss) from continuing operations

'

'

'

'

'

'

'

'

'

328,889,000

589,665,000

-532,757,000

Income from discontinued operations, including gain on sale - net of tax

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss)

'

'

'

'

'

'

'

'

'

'

589,665,000

-532,757,000

Less: Net income attributable to noncontrolling interest

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss) attributable to Arch Coal, Inc.

'

'

'

'

'

'

'

'

'

328,889,000

589,665,000

-532,757,000

Total comprehensive income (loss)

'

'

'

'

'

'

'

'

'

$304,871,000

$595,644,000

($538,841,000)

Supplemental_Consolidating_Fin3

Supplemental Consolidating Financial Information (Schedule of Consolidating Balance Sheets) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
In Thousands, unless otherwise specified
Assets	'	'	'	'
Cash and cash equivalents	$911,099	$784,622	$138,149	$93,593
Restricted cash	'	3,453	'	'
Short term investments	248,414	234,305	'	'
Receivables	229,573	332,080	'	'
Inventories	264,161	365,424	'	'
Other	128,824	194,220	'	'
Total current assets	1,782,071	1,914,104	'	'
Property, plant and equipment, net	6,734,286	7,337,098	'	'
Investment in subsidiaries	'	'	'	'
Intercompany receivables	'	'	'	'
Note receivable from Arch Western	'	'	'	'
Other	473,836	755,575	'	'
Assets, Noncurrent	473,836	755,575	'	'
Total assets	8,990,193	10,006,777	10,213,959	'
Liabilities and Stockholders’ Equity	'	'	'	'
Accounts payable	176,142	224,418	'	'
Accrued expenses and other current liabilities	278,587	319,755	'	'
Current maturities of debt	33,493	32,896	'	'
Total current liabilities	488,222	577,069	'	'
Long-term debt	5,118,002	5,085,879	'	'
Intercompany payables	'	'	'	'
Note payable to Arch Coal	'	'	'	'
Asset retirement obligations	402,713	409,705	'	'
Accrued pension benefits	7,111	67,630	'	'
Accrued postretirement benefits other than pension	39,255	45,086	'	'
Accrued workers’ compensation	78,062	81,629	'	'
Deferred income taxes	413,546	664,182	'	'
Other noncurrent liabilities	190,033	221,030	'	'
Total liabilities	6,736,944	7,152,210	'	'
Stockholders' equity	2,253,249	2,854,567	3,578,040	2,237,507
Total liabilities and stockholders’ equity	8,990,193	10,006,777	'	'
Parent/Issuer [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	799,333	671,313	61,375	13,713
Restricted cash	'	3,453	'	'
Short term investments	248,414	234,305	'	'
Receivables	14,177	49,281	'	'
Inventories	'	'	'	'
Other	84,401	106,786	'	'
Total current assets	1,146,325	1,065,138	'	'
Property, plant and equipment, net	24,851	27,476	'	'
Investment in subsidiaries	7,741,589	8,254,508	'	'
Intercompany receivables	'	'	'	'
Note receivable from Arch Western	675,000	675,000	'	'
Other	162,287	187,171	'	'
Assets, Noncurrent	8,578,876	9,116,679	'	'
Total assets	9,750,052	10,209,293	'	'
Liabilities and Stockholders’ Equity	'	'	'	'
Accounts payable	17,781	19,859	'	'
Accrued expenses and other current liabilities	53,779	65,293	'	'
Current maturities of debt	28,882	32,054	'	'
Total current liabilities	100,442	117,206	'	'
Long-term debt	5,099,833	5,061,925	'	'
Intercompany payables	1,772,624	1,367,739	'	'
Note payable to Arch Coal	'	'	'	'
Asset retirement obligations	1,095	1,646	'	'
Accrued pension benefits	7,797	33,456	'	'
Accrued postretirement benefits other than pension	12,079	13,953	'	'
Accrued workers’ compensation	21,546	25,323	'	'
Deferred income taxes	413,546	664,182	'	'
Other noncurrent liabilities	67,841	69,296	'	'
Total liabilities	7,496,803	7,354,726	'	'
Stockholders' equity	2,253,249	2,854,567	'	'
Total liabilities and stockholders’ equity	9,750,052	10,209,293	'	'
Guarantor Subsidiaries [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	100,418	100,468	75,425	79,880
Restricted cash	'	'	'	'
Short term investments	'	'	'	'
Receivables	23,018	40,452	'	'
Inventories	264,161	365,424	'	'
Other	43,617	86,877	'	'
Total current assets	431,214	593,221	'	'
Property, plant and equipment, net	6,709,398	7,309,550	'	'
Investment in subsidiaries	'	'	'	'
Intercompany receivables	1,953,719	1,600,311	'	'
Note receivable from Arch Western	'	'	'	'
Other	311,463	568,314	'	'
Assets, Noncurrent	2,265,182	2,168,625	'	'
Total assets	9,405,794	10,071,396	'	'
Liabilities and Stockholders’ Equity	'	'	'	'
Accounts payable	158,224	204,370	'	'
Accrued expenses and other current liabilities	228,664	259,162	'	'
Current maturities of debt	4,611	842	'	'
Total current liabilities	391,499	464,374	'	'
Long-term debt	18,169	23,954	'	'
Intercompany payables	'	'	'	'
Note payable to Arch Coal	675,000	675,000	'	'
Asset retirement obligations	401,618	408,059	'	'
Accrued pension benefits	-686	34,174	'	'
Accrued postretirement benefits other than pension	27,176	31,133	'	'
Accrued workers’ compensation	56,516	56,306	'	'
Deferred income taxes	'	'	'	'
Other noncurrent liabilities	121,794	151,360	'	'
Total liabilities	1,691,086	1,844,360	'	'
Stockholders' equity	7,714,708	8,227,036	'	'
Total liabilities and stockholders’ equity	9,405,794	10,071,396	'	'
Non-Guarantor Subsidiaries [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	11,348	12,841	1,349	'
Restricted cash	'	'	'	'
Short term investments	'	'	'	'
Receivables	197,015	247,171	'	'
Inventories	'	'	'	'
Other	806	557	'	'
Total current assets	209,169	260,569	'	'
Property, plant and equipment, net	37	72	'	'
Investment in subsidiaries	'	'	'	'
Intercompany receivables	-181,095	'	'	'
Note receivable from Arch Western	'	'	'	'
Other	86	90	'	'
Assets, Noncurrent	-181,009	90	'	'
Total assets	28,197	260,731	'	'
Liabilities and Stockholders’ Equity	'	'	'	'
Accounts payable	137	189	'	'
Accrued expenses and other current liabilities	781	124	'	'
Current maturities of debt	'	'	'	'
Total current liabilities	918	313	'	'
Long-term debt	'	'	'	'
Intercompany payables	'	232,572	'	'
Note payable to Arch Coal	'	'	'	'
Asset retirement obligations	'	'	'	'
Accrued pension benefits	'	'	'	'
Accrued postretirement benefits other than pension	'	'	'	'
Accrued workers’ compensation	'	'	'	'
Deferred income taxes	'	'	'	'
Other noncurrent liabilities	398	374	'	'
Total liabilities	1,316	233,259	'	'
Stockholders' equity	26,881	27,472	'	'
Total liabilities and stockholders’ equity	28,197	260,731	'	'
Eliminations [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	'	'	'	'
Restricted cash	'	'	'	'
Short term investments	'	'	'	'
Receivables	-4,637	-4,824	'	'
Inventories	'	'	'	'
Other	'	'	'	'
Total current assets	-4,637	-4,824	'	'
Property, plant and equipment, net	'	'	'	'
Investment in subsidiaries	-7,741,589	-8,254,508	'	'
Intercompany receivables	-1,772,624	-1,600,311	'	'
Note receivable from Arch Western	-675,000	-675,000	'	'
Other	'	'	'	'
Assets, Noncurrent	-10,189,213	-10,529,819	'	'
Total assets	-10,193,850	-10,534,643	'	'
Liabilities and Stockholders’ Equity	'	'	'	'
Accounts payable	'	'	'	'
Accrued expenses and other current liabilities	-4,637	-4,824	'	'
Current maturities of debt	'	'	'	'
Total current liabilities	-4,637	-4,824	'	'
Long-term debt	'	'	'	'
Intercompany payables	-1,772,624	-1,600,311	'	'
Note payable to Arch Coal	-675,000	-675,000	'	'
Asset retirement obligations	'	'	'	'
Accrued pension benefits	'	'	'	'
Accrued postretirement benefits other than pension	'	'	'	'
Accrued workers’ compensation	'	'	'	'
Deferred income taxes	'	'	'	'
Other noncurrent liabilities	'	'	'	'
Total liabilities	-2,452,261	-2,280,135	'	'
Stockholders' equity	-7,741,589	-8,254,508	'	'
Total liabilities and stockholders’ equity	($10,193,850)	($10,534,643)	'	'

Supplemental_Consolidating_Fin4

Supplemental Consolidating Financial Information (Schedule of Consolidating Statements of Cash Flows) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash provided by (used in) operating activities	$55,742	$332,804	$642,242
Investing Activities	'	'	'
Payments to Acquire Businesses, Net of Cash Acquired	'	0	2,894,339
Increase (Decrease) in Restricted Cash and Investments	'	'	-5,167
Capital expenditures	-296,984	-395,225	-540,936
Additions to prepaid royalties	-14,947	-13,269	-29,957
Proceeds from dispositions of property, plant and equipment	10,790	22,825	25,887
Proceeds from sale-leaseback transactions	34,919	'	'
Proceeds from sale of Canyon Fuel	422,663	'	'
Investments in and advances to affiliates	-15,260	-17,758	-61,909
Purchases of short term investments	-213,726	-236,862	'
Proceeds from Sale of Short-term Investments	194,537	1,754	'
Change in restricted cash	3,453	6,869	5,167
Purchase of noncontrolling interest	0	'	0
Payments for (Proceeds from) Previous Acquisition	'	0	-829
Cash provided by (used in) investing activities	125,445	-649,166	-3,496,916
Financing Activities	'	'	'
Proceeds from Contributions from Parent	'	'	'
Proceeds from Issuance of Long-term Debt	644,000	1,993,253	'
Proceeds from issuance of senior notes	350,000	359,753	2,000,000
Proceeds from the issuance of common stock, net	'	0	1,267,933
Payments to retire debt	-629,172	-452,934	-605,178
Payments on term loan	-17,250	-7,625	'
Net decrease in borrowings under lines of credit	'	-481,300	424,396
Net payments on other debt	-6,324	-682	5,334
Debt financing costs	-20,489	-50,568	-114,823
Dividends paid	-25,475	-42,440	-80,748
Proceeds from exercise of options under incentive plans	'	5,131	2,316
Transactions with affiliates, net	'	'	'
Cash provided by (used in) financing activities	-54,710	962,835	2,899,230
Increase in cash and cash equivalents	126,477	646,473	44,556
Cash and cash equivalents, beginning of period	784,622	138,149	93,593
Cash and cash equivalents, end of period	911,099	784,622	138,149
Parent/Issuer [Member]	'	'	'
Cash provided by (used in) operating activities	-632,060	-571,576	-187,039
Investing Activities	'	'	'
Payments to Acquire Businesses, Net of Cash Acquired	'	'	2,894,339
Increase (Decrease) in Restricted Cash and Investments	'	'	-5,167
Capital expenditures	-3,320	-4,424	-12,809
Additions to prepaid royalties	'	'	'
Proceeds from dispositions of property, plant and equipment	'	'	'
Proceeds from sale-leaseback transactions	'	'	'
Proceeds from sale of Canyon Fuel	'	'	'
Investments in and advances to affiliates	-5,451	-6,287	-633,534
Purchases of short term investments	-213,726	-236,862	'
Proceeds from Sale of Short-term Investments	194,537	1,754	'
Change in restricted cash	3,453	6,869	'
Payments for (Proceeds from) Previous Acquisition	'	'	-829
Cash provided by (used in) investing activities	-24,507	-256,450	-3,536,344
Financing Activities	'	'	'
Proceeds from Contributions from Parent	'	'	'
Proceeds from Issuance of Long-term Debt	644,000	1,993,253	'
Proceeds from issuance of senior notes	'	'	2,000,000
Proceeds from the issuance of common stock, net	'	'	1,267,933
Payments to retire debt	-628,660	'	'
Payments on term loan	-17,250	-7,625	'
Net decrease in borrowings under lines of credit	'	-375,000	375,000
Net payments on other debt	-6,324	-682	5,334
Debt financing costs	-19,864	-50,022	-114,799
Dividends paid	-25,475	-42,440	-80,748
Proceeds from exercise of options under incentive plans	'	5,131	2,316
Transactions with affiliates, net	838,160	-84,651	316,009
Cash provided by (used in) financing activities	784,587	1,437,964	3,771,045
Increase in cash and cash equivalents	128,020	609,938	47,662
Cash and cash equivalents, beginning of period	671,313	61,375	13,713
Cash and cash equivalents, end of period	799,333	671,313	61,375
Guarantor Subsidiaries [Member]	'	'	'
Cash provided by (used in) operating activities	637,193	781,551	998,082
Investing Activities	'	'	'
Payments to Acquire Businesses, Net of Cash Acquired	'	'	'
Increase (Decrease) in Restricted Cash and Investments	'	'	'
Capital expenditures	-293,664	-390,801	-528,021
Additions to prepaid royalties	-14,947	-13,269	-29,957
Proceeds from dispositions of property, plant and equipment	10,790	1,328	25,887
Proceeds from sale-leaseback transactions	34,919	'	'
Proceeds from sale of Canyon Fuel	422,663	'	'
Investments in and advances to affiliates	-10,321	-13,134	-33,553
Purchases of short term investments	'	'	'
Proceeds from Sale of Short-term Investments	'	'	'
Change in restricted cash	'	'	'
Payments for (Proceeds from) Previous Acquisition	'	'	'
Cash provided by (used in) investing activities	149,440	-415,876	-565,644
Financing Activities	'	'	'
Proceeds from Contributions from Parent	512	1,663	605,178
Proceeds from issuance of senior notes	'	'	'
Proceeds from the issuance of common stock, net	'	'	'
Payments to retire debt	-512	-452,934	-605,178
Payments on term loan	'	'	'
Net decrease in borrowings under lines of credit	'	'	-56,904
Net payments on other debt	'	'	'
Debt financing costs	'	'	-16
Dividends paid	'	'	'
Proceeds from exercise of options under incentive plans	'	'	'
Transactions with affiliates, net	-786,683	110,639	-379,973
Cash provided by (used in) financing activities	-786,683	-340,632	-436,893
Increase in cash and cash equivalents	-50	25,043	-4,455
Cash and cash equivalents, beginning of period	100,468	75,425	79,880
Cash and cash equivalents, end of period	100,418	100,468	75,425
Non-Guarantor Subsidiaries [Member]	'	'	'
Cash provided by (used in) operating activities	50,609	122,829	-168,801
Investing Activities	'	'	'
Payments to Acquire Businesses, Net of Cash Acquired	'	'	'
Increase (Decrease) in Restricted Cash and Investments	'	'	'
Capital expenditures	'	'	-106
Additions to prepaid royalties	'	'	'
Proceeds from dispositions of property, plant and equipment	'	21,497	'
Proceeds from sale-leaseback transactions	'	'	'
Proceeds from sale of Canyon Fuel	'	'	'
Investments in and advances to affiliates	'	'	'
Purchases of short term investments	'	'	'
Proceeds from Sale of Short-term Investments	'	'	'
Change in restricted cash	'	'	'
Payments for (Proceeds from) Previous Acquisition	'	'	'
Cash provided by (used in) investing activities	'	21,497	-106
Financing Activities	'	'	'
Proceeds from Contributions from Parent	'	'	'
Proceeds from issuance of senior notes	'	'	'
Proceeds from the issuance of common stock, net	'	'	'
Payments to retire debt	'	'	'
Payments on term loan	'	'	'
Net decrease in borrowings under lines of credit	'	-106,300	106,300
Net payments on other debt	'	'	'
Debt financing costs	-625	-546	-8
Dividends paid	'	'	'
Proceeds from exercise of options under incentive plans	'	'	'
Transactions with affiliates, net	-51,477	-25,988	63,964
Cash provided by (used in) financing activities	-52,102	-132,834	170,256
Increase in cash and cash equivalents	-1,493	11,492	1,349
Cash and cash equivalents, beginning of period	12,841	1,349	'
Cash and cash equivalents, end of period	11,348	12,841	1,349
Eliminations [Member]	'	'	'
Cash provided by (used in) operating activities	'	'	'
Investing Activities	'	'	'
Payments to Acquire Businesses, Net of Cash Acquired	'	'	'
Increase (Decrease) in Restricted Cash and Investments	'	'	'
Capital expenditures	'	'	'
Additions to prepaid royalties	'	'	'
Proceeds from dispositions of property, plant and equipment	'	'	'
Proceeds from sale-leaseback transactions	'	'	'
Proceeds from sale of Canyon Fuel	'	'	'
Investments in and advances to affiliates	512	1,663	605,178
Purchases of short term investments	'	'	'
Proceeds from Sale of Short-term Investments	'	'	'
Change in restricted cash	'	'	'
Payments for (Proceeds from) Previous Acquisition	'	'	'
Cash provided by (used in) investing activities	512	1,663	605,178
Financing Activities	'	'	'
Proceeds from Contributions from Parent	-512	-1,663	-605,178
Proceeds from issuance of senior notes	'	'	'
Proceeds from the issuance of common stock, net	'	'	'
Payments to retire debt	'	'	'
Payments on term loan	'	'	'
Net decrease in borrowings under lines of credit	'	'	'
Net payments on other debt	'	'	'
Debt financing costs	'	'	'
Dividends paid	'	'	'
Proceeds from exercise of options under incentive plans	'	'	'
Transactions with affiliates, net	'	'	'
Cash provided by (used in) financing activities	-512	-1,663	-605,178
Increase in cash and cash equivalents	'	'	'
Cash and cash equivalents, beginning of period	'	'	'
Cash and cash equivalents, end of period	'	'	'

Valuation_and_Qualifying_Accou1

Valuation and Qualifying Accounts (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Other assets — other notes and accounts receivable	'	'	'
Valuation and Qualifying Accounts Disclosure [Line Items]	'	'	'
Balance at Beginning of Year	$1,043	$17	$0
Additions (Reductions) Charged to Costs and Expenses	346	1,039	17
Charged to Other Accounts	0	0	0
Deductions	614	13	0
Balance at End of Year	775	1,043	17
Current assets — supplies and inventory	'	'	'
Valuation and Qualifying Accounts Disclosure [Line Items]	'	'	'
Balance at Beginning of Year	12,589	13,107	12,701
Additions (Reductions) Charged to Costs and Expenses	503	1,961	1,755
Charged to Other Accounts	-2,274	0	0
Deductions	2,372	2,479	1,349
Balance at End of Year	8,446	12,589	13,107
Deferred income taxes	'	'	'
Valuation and Qualifying Accounts Disclosure [Line Items]	'	'	'
Balance at Beginning of Year	34,663	2,831	737
Additions (Reductions) Charged to Costs and Expenses	8,659	31,832	2,416
Charged to Other Accounts	0	0	0
Deductions	0	0	322
Balance at End of Year	$43,322	$34,663	$2,831