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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2011	Mar. 28, 2012
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2011
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	FY
Entity Registrant Name	ARCH WESTERN RESOURCES LLC
Entity Central Index Key	0001255895
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	No
Entity Filer Category	Non-accelerated Filer
Entity Public Float	$ 0
B.P. p.l.c. [Member]
Membership Interests Percentage		0.50%
Arch Western Acquisition Corporation [Member]
Membership Interests Percentage		99.50%

Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
Consolidated Statements of Income - USD ($) $ in Thousands	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenues	$ 2,261,728	$ 2,048,287	$ 1,651,389
Costs, expenses and other
Cost of sales	1,812,458	1,679,872	1,398,663
Depreciation, depletion and amortization	158,961	167,260	159,755
Amortization of acquired sales contracts, net	19,458	35,606	19,623
Selling, general and administrative expenses	34,313	35,989	44,513
Other operating income, net	(5,974)	(4,789)	(10,475)
Total costs, expenses and other	2,019,216	1,913,938	1,612,079
Income from operations	242,512	134,349	39,310
Interest income (expense), net:
Interest expense	(41,503)	(61,614)	(67,605)
Interest income, primarily from Arch Coal, Inc.	54,312	52,444	46,571
Interest income (expense), net	12,809	(9,170)	(21,034)
Other non-operating expense:
Net loss resulting from early retirement of debt		(6,776)
Nonoperating Income (Expense), Total		(6,776)
Net income
Net income	255,321	118,403	18,276
Redeemable Membership Interest [Member]
Net income
Net income	1,157	537	10
Non-Redeemable Membership Interest [Member]
Net income
Net income	$ 254,164	$ 117,866	$ 18,266

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2011	Dec. 31, 2010
ASSETS
Cash and cash equivalents	$ 75,093	$ 79,817
Receivables	4,964	2,015
Receivable from Arch Coal, Inc.	473,803	582,384
Inventories	170,439	150,419
Other	22,162	21,435
Total current assets	746,461	836,070
Property, plant and equipment
Coal lands and mineral rights	763,059	763,059
Plant and equipment	1,798,404	1,665,285
Deferred mine development	577,332	548,776
Property, plant and equipment, gross, total	3,138,795	2,977,120
Less accumulated depreciation, depletion and amortization	(1,624,296)	(1,488,277)
Property, plant and equipment, net	1,514,499	1,488,843
Other assets:
Receivable from Arch Coal, Inc.	1,234,918	910,797
Other	12,955	10,920
Total other assets	1,247,873	921,717
Total assets	3,508,833	3,246,630
LIABILITIES AND MEMBERSHIP INTERESTS
Accounts payable	183,151	121,670
Accrued expenses and other current liabilities	166,762	153,141
Commercial paper		56,904
Total current liabilities	349,913	331,715
Long-term debt	450,971	451,618
Note payable to Arch Coal, Inc.	225,000	225,000
Asset retirement obligations	305,046	301,355
Accrued postretirement benefits other than pension	22,195	23,509
Accrued pension benefits	24,843	23,904
Other noncurrent liabilities	44,104	43,015
Total liabilities	1,422,072	1,400,116
Redeemable membership interest	11,534	10,444
Total liabilities and membership interests	3,508,833	3,246,630
Non-Redeemable Membership Interest [Member]
LIABILITIES AND MEMBERSHIP INTERESTS
Non-redeemable membership interest	$ 2,075,227	$ 1,836,070

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
OPERATING ACTIVITIES
Net income	$ 255,321	$ 118,403	$ 18,276
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation, depletion and amortization	158,961	167,260	159,755
Amortization of acquired sales contracts, net	19,458	35,606	19,623
Net loss resulting from early retirement of debt		6,776
Amortization relating to financing activities	483	941	964
Changes in operating assets and liabilities:
Receivables	(2,950)	6,364	(5,115)
Inventories	(20,020)	15,230	(11,233)
Accounts payable and accrued expenses	68,392	54,378	(32,439)
Asset retirement obligation	96	22,610	18,328
Other	(14,496)	10,808	9,960
Cash provided by operating activities	465,245	438,376	178,119
INVESTING ACTIVITIES
Capital expenditures	(174,580)	(102,612)	(125,454)
Change in receivable from Arch Coal, Inc.	(234,651)	12,803	(32,784)
Proceeds from dispositions of property, plant and equipment	156	79	91
Additions to prepaid royalties	(3,974)	(2,974)	(2,791)
Reimbursement of deposits on equipment			3,209
Cash used in investing activities	(413,049)	(92,704)	(157,729)
FINANCING ACTIVITIES
Payments to retire debt		(505,627)
Loan from Arch Coal, Inc.		225,000
Net proceeds from (repayments on) commercial paper	(56,904)	7,452	(16,219)
Debt financing costs	(16)	(390)	(203)
Contribution from redeemable membership interest		891
Cash used in financing activities	(56,920)	(272,674)	(16,422)
Increase (decrease) in cash and cash equivalents	(4,724)	72,998	3,968
Cash and cash equivalents, beginning of period	79,817	6,819	2,851
Cash and cash equivalents, end of period	75,093	79,817	6,819
Supplemental cash flow information:
Cash paid during the year for interest, net of amounts capitalized	$ 37,738	$ 71,600	$ 65,626

Consolidated Statements of Non-Redeemable Membership Interest - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Comprehensive income
Net income	$ 255,321	$ 118,403	$ 18,276
Non-Redeemable Membership Interest [Member]
Balance	1,836,070	1,706,710	1,495,613
Comprehensive income
Net income	254,164	117,866	18,266
Pension, postretirement and other post-employment benefits adjustment	(13,241)	13,282	14,998
Net pension, postretirement and other post-employment benefits adjustments reclassified to income	(1,671)	(1,693)	(161)
Total comprehensive income	239,252	129,455	33,103
Reclassification of prior contribution			(121)
Contribution of former Jacob's Ranch mining complex net assets from Arch Coal			178,210
Dividends on preferred membership interest	(95)	(95)	(95)
Balance	$ 2,075,227	$ 1,836,070	$ 1,706,710

Formation of the Company	12 Months Ended
Formation of the Company	Dec. 31, 2011
Formation of the Company
Formation of the Company	1. Formation of the Company On June 1, 1998, Arch Coal, Inc. ("Arch Coal") acquired the Colorado and Utah coal operations of Atlantic Richfield Company ("ARCO") and simultaneously combined the acquired ARCO operations and Arch Coal's Wyoming operation with ARCO's Wyoming operations in a new joint venture named Arch Western Resources, LLC (the "Company"). ARCO was acquired by BP p.l.c. (formerly BP Amoco) in 2000. Arch Coal has a 99.5% common membership interest in the Company, while BP p.l.c. has a 0.5% common membership interest and a preferred membership interest in the Company. Net profits and losses are allocated only to the common membership interests on the basis of 99.5% to Arch Coal and 0.5% to BP p.l.c. In accordance with the membership agreement of the Company, no profit or loss is allocated to the preferred membership interest of BP p.l.c. Except for a preferred return, distributions to members are allocated on the basis of 99.5% to Arch Coal and 0.5% to BP p.l.c. The preferred return entitles BP p.l.c. to receive an annual distribution from the common membership interests equal to 4% of the preferred capital account balance at the end of the year. The preferred return is payable at the Company's discretion. In connection with the formation of the Company, Arch Coal agreed to indemnify BP p.l.c. against certain tax liabilities in the event that such liabilities arise as a result of certain actions taken by Arch Coal or the Company prior to June 1, 2013. The provisions of the indemnification agreement may restrict the Company's ability to sell or dispose of certain properties, repurchase certain of its equity interests or reduce its indebtedness. On October 1, 2009, Arch Coal contributed to the Company the employees, inventories and supply parts, equipment and other personal property of the former Jacobs Ranch mining complex, which was adjacent to the Company's Black Thunder mining operations. The contributed assets and related liabilities were immediately merged with the Black Thunder mining operations. The Company is leasing the related coal reserves of approximately 345 million tons from a subsidiary of Arch Coal.

Accounting Policies	12 Months Ended
Accounting Policies	Dec. 31, 2011
Accounting Policies
Accounting Policies	2. Accounting Policies *Basis of Presentation* The consolidated financial statements include the accounts of the Company and its subsidiaries and controlled entities. Intercompany transactions and accounts have been eliminated in consolidation. The Company produces coal from surface and underground mines for sale to domestic and international customers as steam coal to power plants and industrial facilities. The Company's mines are located in Wyoming, Colorado and Utah. The Company's results of operations reflect all costs of doing business, including expenses incurred on the Company's behalf by Arch Coal. Certain assets, such as coal reserves and acquired sales contracts, may be owned by and reflected in the financial statements of Arch Coal, but the cost representing the usage of those assets is reflected in the results of operations of the Company. In addition, there is goodwill of $115.8 million on the consolidated balance sheet of Arch Coal that is associated with the Company's Powder River Basin segment for Arch Coal's impairment testing purposes. *Accounting Pronouncements* There were 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 disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. 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. *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 prior to title transfer 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. *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. Sales contracts associated with the acquisition of the Jacob's Ranch mining complex were not contributed to the Company, however, the amortization of these acquired sales contracts is reflected in the accompanying consolidated statements of income. Based upon expected shipments under these contracts in the next five years, the Company anticipates annual amortization expense (income) of acquired sales contracts in the next five years of: $0.7 million, $(4.7) million, $(4.7) million, $(4.8) million and $0.4 million. *Property, Plant and Equipment* Plant and Equipment Plant and equipment are recorded at cost. Interest costs applicable to major asset additions are capitalized during the construction period. 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 on 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 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 costs associated with asset retirement obligations. Coal Lands and Mineral Rights A significant portion of the Company's coal reserves are controlled through leasing arrangements, primarily with Arch Coal. The net book value of the Company's leased coal interests was $332.3 million and $339.9 million at December 31, 2011 and 2010, respectively. Any amounts paid to acquire coal reserves are capitalized 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. The leases 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. 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. *Revenue Recognition* Revenues include sales to customers of coal produced at Company operations. 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 income in the accompanying consolidated statements of income reflects income and expense from sources other than coal sales. 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 discounted cash flow 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 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 10, "Asset Retirement Obligations." Income Taxes The financial statements do not include a provision for income taxes as the Company is treated as a partnership for income tax purposes and does not incur federal or state income taxes. Instead, its earnings and losses are included in the members' separate income tax returns. Related Party Transactions Transactions with Arch Coal may not be at arms length. If the transactions were negotiated with an unrelated party, the impact could be material to the Company's results of operations. See Note 11, "Related Party Transactions" for discussion of various transactions with Arch Coal. Benefit Plans** Essentially all of the Company's employees are covered by Arch Coal's non-contributory defined benefit pension plan. The benefits are based on the employee's age and compensation. The Company also provides certain postretirement medical and life insurance benefits for eligible employees under Arch Coal's plans. The Company reflects its actuarially-determined allocation of benefit cost, benefit obligation and other comprehensive income related to these plans in its consolidated financial statements. See further discussion in Note 9, "Employee Benefit Plans."

Redeemable Membership Interest

12 Months Ended

Dec. 31, 2011

B.P. p.l.c. [Member]

Redeemable Membership Interest

3. Redeemable Membership Interest

The terms of the Company's membership agreement grant a put right to BP p.l.c., where BP p.l.c. may require Arch Coal to purchase its membership interest. The terms of the agreement state that the price of the membership interest shall be determined by mutual agreement between the members. In the absence of an agreed-upon price, the price is equal to the sum of the preferred membership interest of $2.4 million and BP p.l.c.'s common membership interest, as defined in the agreement. In addition, Arch Coal has a call right, which allows Arch Coal to purchase BP p.l.c.'s members' interest as long as it pays damages as set forth in the agreement between the members.

The following table presents the components of and changes in BP p.l.c.'s membership interest:

	Common Membership Interest	Preferred Membership Interest	Total Redeemable Membership Interest
	(In thousands)
Balance at January 1, 2009	$ 6,366	$ 2,399	$ 8,765
Net income attributable to BP p.l.c. common membership interest	10	—	10
Other comprehensive income attributable to BP p.l.c. common membership interest	67	—	67
Reclassification of prior contribution	121	—	121
Dividends on preferred membership interest	(1)	—	(1)
Balance at December 31, 2009	6,563	2,399	8,962
Net income attributable to BP p.l.c. common membership interest	537	—	537
Other comprehensive income attributable to BP p.l.c. common membership interest	55	—	55
BP p.l.c's contribution related to Jacobs Ranch	891	—	891
Dividends on preferred membership interest	(1)	—	(1)
Balance at December 31, 2010	8,045	2,399	10,444
Net income attributable to BP p.l.c. common membership interest	1,157	—	1,157
Other comprehensive income attributable to BP p.l.c. common membership interest	(66)	—	(66)
Dividends on preferred membership interest	(1)	—	(1)
Balance at December 31, 2011	$ 9,135	$ 2,399	$ 11,534

- Definition

The entire disclosure for the formation, structure, control and ownership of the partnership. Disclosures related to accounts comprising partners' capital. Includes balances of general partners' capital account, limited partners' capital account, preferred partners' capital account and total partners' capital account and units outstanding; accumulated other comprehensive income; amount and nature of changes to amount of partner's capital and units outstanding by class, rights and privileges for each class of units; distribution policies and distributions paid by unit class; impact of and correction of an error in previously issued financial statements; limitations of partners' liability; redemption, conversion and distribution policies; and deferred compensation related to the issuance of units.

+ References + Details

Accumulated Other Comprehensive Income (Loss)

12 Months Ended

Dec. 31, 2011

Accumulated Other Comprehensive Income (Loss)

Accumulated Other Comprehensive Income (Loss)

4. Accumulated Other Comprehensive Income (Loss)

Other comprehensive income (loss) items are transactions recorded in membership interests during the year, excluding net income and transactions with members. Following are the items included in accumulated other comprehensive income (loss):

	Accumulated Other Comprehensive Income (Loss)
		(In thousands)
Balance at January 1, 2009	$ (24,678)
Pension, postretirement and other post-employment benefits	14,903
Balance at December 31, 2009	(9,775)
Pension, postretirement and other post-employment benefits	11,645
Balance at December 31, 2010	1,870
Pension, postretirement and other post-employment benefits	(14,978)
Balance at December 31, 2011	$ (13,108)

The net losses that is expected to be reclassified from accumulated other comprehensive income into net income 2012 is $2.2 million.

- Definition

The entire disclosure for comprehensive income. Includes, but is not limited to, the following: 1) the amount of income tax expense or benefit allocated to each component of other comprehensive income, including reclassification adjustments, 2) the reclassification adjustments for each classification of other comprehensive income and 3) the ending accumulated balances for each component of comprehensive income. Components of comprehensive income include: (1) foreign currency translation adjustments; (2) gains (losses) on foreign currency transactions that are designated as, and are effective as, economic hedges of a net investment in a foreign entity; (3) gains (losses) on intercompany foreign currency transactions that are of a long-term-investment nature, when the entities to the transaction are consolidated, combined, or accounted for by the equity method in the reporting enterprise's financial statements; (4) change in the market value of a futures contract that qualifies as a hedge of an asset reported at fair value; (5) unrealized holding gains (losses) on available-for-sale securities and that resulting from transfers of debt securities from the held-to-maturity category to the available-for-sale category; (6) a net loss recognized as an additional pension liability not yet recognized as net periodic pension cost; and (7) the net gain (loss) and net prior service cost or credit for pension plans and other postretirement benefit plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 130
-Paragraph 14-26
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=6920043&loc=d3e637-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=6920043&loc=d3e681-108580

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=6920043&loc=d3e653-108580

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=6959260&loc=d3e187085-122770

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 16
-URI http://asc.fasb.org/extlink&oid=6920043&loc=d3e709-108580

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 55
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6920433&loc=d3e998-108581

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=6920043&loc=d3e640-108580

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Reclassification Adjustments
-URI http://asc.fasb.org/extlink&oid=6522872

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=6920043&loc=d3e716-108580

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=6920043&loc=d3e689-108580

+ Details

Inventories

12 Months Ended

Dec. 31, 2011

Inventories

Inventories

5. Inventories

Inventories consist of the following:

	December 31
	2011	2010
	(In thousands)
Coal	$ 65,790	$ 46,464
Repair parts and supplies, net of allowance	104,649	103,955
	$170,439	$150,419

The repair parts and supplies are stated net of an allowance for slow-moving and obsolete inventories of $12.1 million and $11.7 million at December 31, 2011 and 2010, respectively.

Accrued Expenses and Other Current Liabilities

12 Months Ended

Dec. 31, 2011

Accrued Expenses and Other Current Liabilities [Abstract]

Acrrued Expenses and Other Current Liabilities

6. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consists of the following:

	December 31
	2011	2010
	(In thousands)
Payroll and employee benefits	$ 22,606	$ 24,971
Taxes	110,578	98,914
Interest	16,804	17,189
Other	16,774	12,067
	$166,762	$153,141

Debt and Financing Arrangments	12 Months Ended
Debt and Financing Arrangments	Dec. 31, 2011
Debt and Financing Arrangements
Debt and Financing Arrangements	7. Debt and Financing Arrangements Commercial paper On June 14, 2011, the Company terminated its commercial paper placement program and the supporting credit facility. 2013 Senior Notes The 6.75% senior notes, due July 1, 2013, ("2013 Notes") were issued by the Company's subsidiary, Arch Western Finance LLC ("Arch Western Finance"), under an indenture dated June 25, 2003. The senior notes are guaranteed by Arch Western and certain of its subsidiaries and are secured by an intercompany note from Arch Coal. The Company redeemed $500.0 million aggregate principal amount of the 2013 Notes on September 8, 2010. The Company recognized a loss on the redemption of $6.8 million, including the payment of the $5.6 million redemption premium and the write-off of $3.3 million of unamortized debt financing costs, partially offset by the write-off of $2.1 million of the original issue premium. The Company funded this redemption with cash transferred from Arch Coal in the form of a loan of $225.0 million and a repayment of a portion of the note receivable from Arch Coal. The terms of the 2013 Notes contain restrictive covenants that limit Arch Western's ability to, among other things, incur additional debt, sell or transfer assets, pay dividends and make certain investments. Of the aggregate principal outstanding at December 31, 2011 and 2010, $118.4 million of the 2013 Notes were issued at a premium of 104.75% of par. The premium is being amortized over the term of the notes. Interest is payable on the notes on January 1 and July 1 of each year. The notes are redeemable at any time at their face value. The $225.0 million loan was made pursuant to an intercompany credit agreement with Arch Coal. Under the intercompany credit agreement, the Company may borrow up to $675.0 million through July 1, 2013, or such later date as designated by Arch Coal. Interest on loans outstanding under the agreement is calculated at a per annum rate equal to the three month LIBOR rate plus 200 or 250 basis points, depending on the Company's leverage ratio, as defined in the agreement, at the date the rate is determined. As of December 31, 2011and 2010, the interest rate on the loan was 2.87% and 2.79%, respectively. Interest is due on any outstanding loans on the first day of each calendar quarter. The Company may repay the balance of the loan at any time, in whole or in part, without penalty. It is currently management's intention not to prepay the balance of the loan within the next year. Therefore, the loan is classified on the accompanying consolidated balance sheets as noncurrent.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References + Details

Fair Values of Financial Instruments	12 Months Ended
Fair Values of Financial Instruments	Dec. 31, 2011
Fair Values of Financial Instruments
Fair Values of Financial Instruments	8. Fair Values of Financial Instruments The following methods and assumptions were used by the Company in estimating its fair value disclosures for financial instruments: Cash and cash equivalents: At December 31, 2011 and 2010, the carrying amounts of cash and cash equivalents approximate fair value. Debt: The fair value of the Company's debt, excluding intercompany debt, was $ 451.7 million and $512.5 million at December 31, 2011 and 2010, respectively. Fair values are based upon observed prices in an active market when available or from valuation models using market information.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44A, 44B
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 15C, 15D
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Name Statement of Financial Accounting Standard (FAS)
-Number 107
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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-Name Statement of Financial Accounting Standard (FAS)
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
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Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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+ Details

Employee Benefit Plans

12 Months Ended

Dec. 31, 2011

Employee Benefit Plans

Employee Benefit Plans

9. Employee Benefit Plans

Defined Benefit Pension and Other Postretirement Benefit Plans

Essentially all of the Company's employees are covered by Arch Coal's defined benefit pension plan. The benefits are based on the employee's age and compensation. Arch Coal 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 federal income tax purposes. Arch Coal allocates a portion of the funding to the Company, which is charged to the intercompany receivable. See Note 11, "Related Party Transactions" for further discussion.

The Company also provides certain postretirement medical/life insurance benefits for eligible employees under Arch Coal's plans. Generally, covered employees who terminate employment after meeting eligibility requirements are eligible for postretirement coverage for themselves and their dependents. The employee postretirement medical/life plans are contributory, with retiree contributions adjusted periodically, and contain other cost-sharing features such as deductibles and coinsurance. Arch Coal allocates a portion of the funding to the Company, which is charged to the intercompany receivable as benefits are paid.

The Company's allocated expense related to these plans was $8.4 million, $9.6 million and $12.6 million for the years ended December 31, 2011, 2010 and 2009, respectively. The Company's balance sheet reflects its allocated portion of Arch Coal's liabilities related to its benefit plans, including amounts recorded through other comprehensive income. The Company's recorded balance sheet amounts are as follows:

	December 31
	2011		2010
	(In thousands)
Accrued benefit liabilities (current)	$ 2,115	$ 1,230
Accrued benefit liabilities (noncurrent)	47,038	47,413
Accumulated other comprehensive loss	(14,540)	(21)

Other Plans

Arch Coal sponsors savings plans that have been established to assist eligible employees in providing for their future retirement needs. The Company's expense related to the plans were $12.1 million in 2011, $11.4 million in 2010 and $9.5 million in 2009.

- Definition

The entire disclosure for pension and other postretirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 132R
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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-Name Statement of Financial Accounting Standard (FAS)
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
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Reference 6: http://www.xbrl.org/2003/role/presentationRef
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Reference 7: http://www.xbrl.org/2003/role/presentationRef
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Principles Board Opinion (APB)
-Number 30
-Paragraph 26
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Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 132R
-Paragraph 5, 6, 7, 8
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Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Implementation Guide (Q and A)
-Number FAS88
-Paragraph 63
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Reference 14: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 715
-URI http://asc.fasb.org/topic&trid=2235017

+ Details

Asset Retirement Obligations

12 Months Ended

Dec. 31, 2011

Asset Retirement Obligation [Abstract]

Asset Retirement Obligations

10. 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
	2011	2010
	(In thousands)
Balance at January 1 (including current portion)	$ 308,395	$ 277,088
Accretion expense	26,541	23,952
Adjustments to the liability from changes in estimates	9,682	8,831
Liabilities settled	(25,932)	(1,476)
Balance at December 31	318,686	308,395
Current portion included in accrued expenses	(13,640)	(7,040)
Noncurrent liability	$ 305,046	$ 301,355

Liabilities settled of $25.9 million in 2011 mostly related to reclamation activities at the Black Thunder mining complex on a pit acquired with the Jacobs Ranch operations in 2009.

As of December 31, 2011, the Company had $34.0 million in surety bonds outstanding and $417.7 million in self-bonding to secure reclamation obligations.

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2011
Related Party Transactions
Related Party Transactions	11. Related Party Transactions The Company's cash transactions are managed by Arch Coal. Cash paid to or from the Company that is not considered a distribution or a contribution is recorded in an Arch Coal receivable account. In addition, any amounts owed between the Company and Arch Coal, exclusive of borrowings under the intercompany credit agreement discussed in Note 7, "Debt and Financing Arrangements", are recorded in the account. The receivable from Arch Coal was approximately $1.7 billion and $1.5 billion, at December 31, 2011 and 2010, respectively. This amount earns interest from Arch Coal at the prime interest rate. Interest earned for the years ended December 31, 2011, 2010 and 2009 was $54.3 million, $52.2 million and $46.5 million, respectively. The current portion of the receivable balance at December 31, 2011 represents the amount needed to fund working capital and contractual purchase, service and lease obligations due within the next twelve months. As mentioned in Note 7, "Debt and Financing Arrangements", during September of 2010, the Company received a loan of $225.0 million and a repayment of a portion of the balance receivable from Arch Coal to redeem $500.0 million aggregate principal amount of the outstanding 2013 Notes at a redemption price of 101.125%. Interest incurred on the loan was $6.3 million and $1.9 million for the years ended December 31, 2011 and 2010, respectively. On February 10, 2006, Arch Coal established an accounts receivable securitization program. Under the program, the Company sells its receivables to Arch Coal without recourse at a discount based on the prime rate and days sales outstanding. During 2011, 2010 and 2009, the Company sold $1.7 billion, $1.7 billion and $1.4 billion of trade accounts receivable to Arch Coal, respectively, at a discount of $3.7 million, $4.0 million and $3.5 million, respectively. The Company mines on tracts that are owned or leased by Arch Coal and subleased to the Company. Approximately 70% of the Company's reserves are controlled under a lease with Arch Coal. Royalties on all properties leased from Arch Coal are 7.0% of the value of the coal mined and removed from the leased land, pursuant to Federal coal regulations, plus all rents and royalties (excluding bonus bid obligations) due under Arch Coal's subsidiary's state and federal lease agreements. No advance royalties are required under the agreements. For the years ended December 31, 2011, 2010 and 2009, the Company incurred production royalties of $102.8 million, $92.4 million and $47.8 million, respectively, under sublease agreements with Arch Coal. Amounts charged to the intercompany account for the Company's allocated portion of contributions to the Arch Coal, Inc. Retirement Account Plan and to the Arch Coal, Inc. Postretirement Benefit Plan totaled $22.4 million, $10.9 million and $11.1 million for the years ended December 31, 2011, 2010 and 2009, respectively. The Company is charged selling, general and administrative services fees by Arch Coal. Expenses are allocated based on Arch Coal's best estimates of proportional or incremental costs, whichever is more representative of costs incurred by Arch Coal on behalf of the Company. Amounts allocated to the Company by Arch Coal were $34.3 million, $36.0 million and $44.5 million for the years ended December 31, 2011, 2010 and 2009, respectively. Costs allocated in 2009 included costs related to the Jacobs Ranch acquisition. Such amounts are reported as selling, general and administrative expenses in the accompanying consolidated statements of income.

- Definition

The entire disclosure for related party transactions, including the nature of the relationship(s), a description of the transactions, the amount of the transactions, the effects of any change in the method of establishing the terms of the transaction from the previous period, stated interest rate, expiration date, terms and manner of settlement per the agreement with the related party, and amounts due to or from related parties. If the entity and one or more other entities are under common ownership or management control and this control affects the operating results or financial position, disclosure includes the nature of the control relationship even if there are no transactions between the entities. Disclosure may also include the aggregate amount of current and deferred tax expense for each statement of earnings presented where the entity is a member of a group that files a consolidated tax return, the amount of any tax related balances due to or from affiliates as of the date of each statement of financial position presented, the principal provisions of the method by which the consolidated amount of current and deferred tax expense is allocated to the members of the group and the nature and effect of any changes in that method. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 4
-Section 08
-Paragraph k

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 3A
-Section 04
-Paragraph b

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 57
-Paragraph 1-4
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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+ Details

Concentration of Credit Risk and Major Customers

12 Months Ended

Dec. 31, 2011

Concentration of Credit Risk and Major Customers [Abstract]

Concentration of Credit Risk and Major Customers

12. Concentration of Credit Risk and Major Customers

The Company markets its steam coal principally to electric utilities in the United States. Revenues from export sales were $167,097 in 2011, $40,949 in 2010 and $50,150 in 2009. Arch Coal has a formal written credit policy that establishes procedures to determine creditworthiness and credit limits for trade customers. 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 is committed under long-term contracts to supply coal that meets certain quality requirements at specified prices. These prices are generally adjusted based on 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 and its operating subsidiaries sold approximately 132.0 million tons of coal in 2011. Approximately 77% of this tonnage (representing approximately 77% 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 six years. Some of these contracts include pricing which is above current market prices. Sales (including spot sales) to significant customers were as follows:

	Year Ended December 31
	2011	2010	2009
	(In thousands)
Ameren	$ 119,212	$220,937	$189,768

Transportation

The Company depends upon 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 and result in decreased shipments. In the past, disruptions in rail service have resulted in missed shipments and production interruptions.

- Definition

The entire disclosure for any concentrations existing at the date of the financial statements that make an entity vulnerable to a reasonably possible, near-term, severe impact. This disclosure informs financial statement users about the general nature of the risk associated with the concentration, and may indicate the percentage of concentration risk as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 15A
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Statement of Position (SOP)
-Number 94-6
-Paragraph 21, 22, 24
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+ Details

Leases

12 Months Ended

Dec. 31, 2011

Leases [Abstract]

Leases

13. 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, 2011 are as follows:

	Operating Leases	Royalties
	(In thousands)
2012	$ 23,506	$ 1,203
2013	22,698	1,117
2014	20,679	1,071
2015	14,701	938
2016	8,257	758
Thereafter	9,164	7,092
	$ 99,005	$ 12,179

Rental expense related to these operating leases amounted to $31.2 million in 2011, $32.3 million in 2010 and $33.5 million in 2009. Royalty expense was $345.5 million, $322.3 million and $227.6 million for the years ended December 31, 2011, 2010 and 2009, respectively, including $102.8 million, $92.4 million and $47.8 million, respectively, that were incurred under sublease agreements with Arch Coal. See Note 11, "Related Party Transactions" for further discussion of these agreements.

As of December 31, 2011, certain of the Company's lease obligations were secured by outstanding surety bonds totaling $30.9 million.

- Definition

The entire disclosure for lessee entity's leasing arrangements including, but not limited to, all of the following: (a.) The basis on which contingent rental payments are determined, (b.) The existence and terms of renewal or purchase options and escalation clauses, (c.) Restrictions imposed by lease agreements, such as those concerning dividends, additional debt, and further leasing.

+ References + Details

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2011
Commitments and Contingencies
Commitments and Contingencies	14. Commitments and Contingencies Arch Coal is a party to a number of transportation capacity throughput agreements, to secure port and rail capacity for its export shipments out of the West and Gulf coasts. While the Company is not a party to these agreements if the contracted quantities are not fulfilled, Arch Coal would allocate any charges incurred to the Company. The maximum liquidated damages under these contracts are approximately $45 million in 2012, $46 million in 2013, $47 million in 2014 and $39 million in 2015. The Company is a party to numerous claims and lawsuits with respect to various matters. The Company provides for costs related to contingencies when a loss is probable and the amount is reasonably determinable. After conferring with counsel, it is the opinion of management that the ultimate resolution of pending claims will not have a material adverse effect on the consolidated financial condition, results of operations or liquidity of the Company.

- Definition

The entire disclosure for commitments and contingencies.

+ References

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+ Details

Segment Information

12 Months Ended

Dec. 31, 2011

Segment Information

Segment Information

15. Segment Information

The Company has two reportable business segments, which are based on the major low-sulfur coal basins in which the Company operates. Both of these reportable business segments include a number of mine complexes. The Company manages its coal sales by coal basin, not by individual mine complex. Geology, coal transportation routes to customers, regulatory environments and coal quality are generally consistent within a basin. Accordingly, market and contract pricing have developed by coal basin. Mine 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 Western Bituminous (WBIT) segment, with operations in Utah, Colorado and southern Wyoming.

Operating segment results for the years ended December 31, 2011, 2010 and 2009 are presented below. Results for the operating segments include all direct costs of mining. Corporate, Other and Eliminations includes primarily corporate overhead and other support functions.

The amounts in the Corporate, Other and Eliminations represent primarily intercompany receivables.

	PRB	WBIT	Corporate, Other and Eliminations	Consolidated
	(In thousands)
December 31, 2011
Revenues	$ 1,588,962	$ 672,766	$ —	$ 2,261,728
Income from operations	150,618	121,065	(29,171)	242,512
Total assets	1,108,651	655,169	1,745,013	3,508,833
Depreciation, depletion and amortization	80,852	78,109	—	158,961
Amortization of acquired sales contracts, net	19,458	—	—	19,458
Capital expenditures	108,223	66,357	—	174,580
December 31, 2010
Revenues	$ 1,510,825	$ 537,462	$ —	$ 2,048,287
Income from operations	108,710	58,740	(33,101)	134,349
Total assets	1,064,879	649,843	1,531,908	3,246,630
Depreciation, depletion and amortization	88,784	78,476	—	167,260
Amortization of acquired sales contracts, net	35,606	—	—	35,606
Capital expenditures	37,141	65,471	—	102,612
December 31, 2009
Revenues	$ 1,112,371	$ 539,018	$ —	$ 1,651,389
Income from operations	45,463	31,472	(37,625)	39,310
Total assets	1,051,007	693,972	1,562,934	3,307,913
Depreciation, depletion and amortization	78,174	81,581	—	159,755
Amortization of acquired sales contracts, net	19,934	(311)	—	19,623
Capital expenditures	58,155	67,299	—	125,454

Reconciliation of income from operations to net income:

	Year Ended December 31
	2011	2010	2009
	(In thousands)
Income from operations	$ 242,512	$ 134,349	$ 39,310
Interest expense	(41,503)	(61,614)	(67,605)
Interest income	54,312	52,444	46,571
Net loss resulting from early retirement of debt	—	(6,776)	—
Net income	$ 255,321	$ 118,403	$ 18,276

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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+ Details

Supplemental Condensed Consolidating Financial Information

12 Months Ended

Dec. 31, 2011

Supplemental Condensed Consolidating Financial Information [Abstract]

Supplemental Condensed Consolidating Financial Information

16. Supplemental Condensed Consolidating Financial Information

Pursuant to the indenture governing the Arch Western Finance 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 condensed consolidating financial information for (i) the Company, (ii) the issuer of the senior notes (Arch Western Finance, LLC, a wholly-owned subsidiary of the Company), (iii) the Company's wholly-owned subsidiaries (Thunder Basin Coal Company, LLC, Mountain Coal Company, LLC, and Arch of Wyoming, LLC), on a combined basis, which are guarantors under the Notes, and (iv) the Company's majority-owned subsidiary, Canyon Fuel, which is not a guarantor under the Notes.

Condensed Consolidating Statements of Income
Year Ended December 31, 2011
(In thousands)

	Parent Company	Issuer	Guarantor Subsidiaries	Non-Guarantor Subsidiaries	Eliminations	Consolidated

Revenues	$ –	$ –	$ 1,858,872	$ 402,856	$ –	$ 2,261,728
Cost of sales	(3,592)	–	1,528,551	287,499	–	1,812,458
Depreciation, depletion and amortization	–	–	116,213	42,750	(2)	158,961
Amortization of acquired sales contracts, net	–	–	19,458	–	–	19,458
Selling, general and administrative expenses	34,313	–	–	–	–	34,313
Other operating income, net	(1,562)	–	(3,578)	(834)	–	(5,974)
	29,159	–	1,660,644	329,415	(2)	2,019,216
Income from investment in subsidiaries	270,520	–	–	–	(270,520)	–

Income from operations	241,361	–	198,228	73,441	(270,518)	242,512
Interest income (expense), net
Interest expense	(40,293)	(30,751)	(136)	(698)	30,375	(41,503)
Interest income	54,251	30,375	–	61	(30,375)	54,312
	13,958	(376)	(136)	(637)	–	12,809

Net income (loss)	$ 255,319	$ (376)	$ 198,092	$ 72,804	$ (270,518)	$ 255,321

Condensed Consolidating Statements of Income
Year Ended December 31, 2010
(In thousands)

	Parent Company	Issuer	Guarantor Subsidiaries	Non-Guarantor Subsidiaries	Eliminations	Consolidated

Revenues	$ –	$ –	$ 1,679,460	$ 368,827	$ –	$ 2,048,287
Cost of sales	(2,422)	–	1,394,853	290,005	(2,564)	1,679,872
Depreciation, depletion and amortization	–	–	119,109	48,151	–	167,260
Amortization of acquired sales contracts, net	–	–	35,606	–	–	35,606
Selling, general and administrative expenses	35,989	–	–	–	–	35,989
Other operating income, net	(467)	–	(3,178)	(3,708)	2,564	(4,789)
	33,100	–	1,546,390	334,448	–	1,913,938
Income from investment in subsidiaries	158,865	–	–	–	(158,865)	–

Income from operations	125,765	–	133,070	34,379	(158,865)	134,349

Interest income (expense), net
Interest expense	(59,435)	(54,280)	–	(774)	52,875	(61,614)
Interest income	52,073	52,875	288	83	(52,875)	52,444
	(7,362)	(1,405)	288	(691)	–	(9,170)
Other non-operating expenses
Net loss resulting from early retirement of debt	–	(6,776)	–	–	–	(6,776)

Net income (loss)	$ 118,403	$(8,181)	$ 133,358	$ 33,688	$ (158,865)	$ 118,403

Condensed Consolidating Statements of Income
Year Ended December 31, 2009
(In thousands)

	Parent Company	Issuer	Guarantor Subsidiaries	Non-Guarantor Subsidiaries	Eliminations	Consolidated

Revenues	$ –	$ –	$1,252,732	$ 398,657	$ –	$ 1,651,389
Cost of sales	647	–	1,102,788	298,240	(3,012)	1,398,663
Depreciation, depletion and amortization	–	–	103,161	56,594	–	159,755
Amortization of acquired sales contracts, net	–	–	19,934	(311)	–	19,623
Selling, general and administrative expenses	44,513	–	–	–	–	44,513
Other operating income, net	(7,549)	–	(2,333)	(3,605)	3,012	(10,475)
	37,611	–	1,223,550	350,918	–	1,612,079
Income from investment in subsidiaries	77,243	–	–	–	(77,243)	–

Income from operations	39,632	–	29,182	47,739	(77,243)	39,310

Interest income (expense), net
Interest expense	(67,666)	(64,095)	981	(950)	64,125	(67,605)
Interest income	46,310	64,125	30	231	(64,125)	46,571
	(21,356)	30	1,011	(719)	–	(21,034)

Net income	$ 18,276	$ 30	$ 30,193	$ 47,020	$ (77,243)	$ 18,276

Condensed Consolidating Balance Sheets
December 31, 2011
(In thousands)

	Parent Company	Issuer	Guarantor Subsidiaries		Non-Guarantor Subsidiaries	Eliminations	Consolidated

Cash and cash equivalents	$ —	$ —	$ 75,058		$ 35	$ —	$ 75,093
Receivables	2,012	—	887		2,065	—	4,964
Receivable from Arch Coal	473,803	—	—		—	—	473,803
Intercompanies	(457,908)	15,188	342,486		100,234	—	—
Inventories	—	—	114,406		56,033	—	170,439
Other	8,820	1,017	6,035		6,290	—	22,162
Total current assets	26,727	16,205	538,872		164,657	—	746,461
Property, plant and equipment, net	—	—	1,248,892		265,620	(13)	1,514,499
Investment in subsidiaries	3,051,144	—	—		—	(3,051,144)	—
Receivable from Arch Coal	1,213,354	—	—		21,564	—	1,234,918
Intercompanies	(1,948,670)	455,385	1,245,698		247,587	—	—
Other	1,369	502	7,066		4,018	—	12,955
Total other assets	2,317,197	455,887	1,252,764		273,169	(3,051,144)	1,247,873
Total assets	$2,343,924	$ 472,092	$ 3,040,528		$ 703,446	$(3,051,157)	$ 3,508,833
Accounts payable	$ 14,754	—	$ 145,793		$ 22,604	$ —	$ 183,151
Accrued expenses and other current liabilities	3,153	15,188	140,836		7,585	—	166,762
Total current liabilities	17,907	15,188	286,629		30,189	—	349,913
Long-term debt	—	450,971	—		—	—	450,971
Note payable to Arch Coal	225,000	—	—		—	—	225,000
Asset retirement obligations	—	—	296,302		8,744	—	305,046
Accrued postretirement benefits other than pension	2,968	—	10,475		8,752	—	22,195
Accrued pension benefits	8,943	—	5,299		10,601	—	24,843
Other noncurrent liabilities	2,332	—	37,563		4,209	—	44,104
Total liabilities	257,150	466,159	636,268		62,495	—	1,422,072
Redeemable membership interest	11,534	—	—		—	—	11,534
Non-redeemable membership interest	2,075,240	5,933		2,404,260	640,951	(3,051,157)	2,075,227
Total liabilities and membership interests	$2,343,924	$472,092		$ 3,040,528	$ 703,446	$(3,051,157)	$ 3,508,833

Condensed Consolidating Balance Sheets
December 31, 2010
(In thousands)

	Parent Company	Issuer	Guarantor Subsidiaries	Non-Guarantor Subsidiaries	Eliminations	Consolidated

Cash and cash equivalents	$ 1,613	$ —	$ 78,070	$ 134	$ —	$ 79,817
Receivables	1,033	—	663	319	—	2,015
Receivable from Arch Coal	582,384	—	—	—	—	582,384
Intercompanies	(519,808)	15,188	341,981	162,639	—	—
Inventories	—	—	104,394	46,025	—	150,419
Other	10,096	1,015	4,129	6,195	—	21,435
Total current assets	75,318	16,203	529,237	215,312	—	836,070
Property, plant and equipment, net	—	—	1,223,493	265,350	—	1,488,843
Investment in subsidiaries	2,789,637	—	—	—	(2,789,637)	—
Receivable from Arch Coal	888,306	—	—	22,491	—	910,797
Intercompanies	(1,609,147)	455,401	1,023,119	130,627	—	—
Other	1,402	1,511	3,802	4,205	—	10,920
Total other assets	2,070,198	456,912	1,026,921	157,323	(2,789,637)	921,717
Total assets	$2,145,516	$ 473,115	$ 2,779,651	$ 637,985	$(2,789,637)	$ 3,246,630
Accounts payable	$ 2,604	$ —	$ 102,290	$ 16,776	$ —	$ 121,670
Accrued expenses and other current liabilities	5,714	15,188	122,473	9,766	—	153,141
Commercial paper	56,904	—	—	—	—	56,904
Total current liabilities	65,222	15,188	224,763	26,542	—	331,715
Long-term debt	—	451,618	—	—	—	451,618
Note payable to Arch Coal	225,000	—	—	—	—	225,000
Asset retirement obligations	—	—	290,473	10,882	—	301,355
Accrued postretirement benefits other than pension	3,629	—	11,571	8,309	—	23,509
Accrued pension benefits	3,342	—	11,962	8,600	—	23,904
Other noncurrent liabilities	1,809	—	36,972	4,234	—	43,015
Total liabilities	299,002	466,806	575,741	58,567	—	1,400,116
Redeemable membership interest	10,444	—	—	—	—	10,444
Non-redeemable membership interest	1,836,070	6,309	2,203,910	579,418	(2,789,637)	1,836,070
Total liabilities and membership interests	$2,145,516	$ 473,115	$ 2,779,651	$ 637,985	$(2,789,637)	$ 3,246,630

Condensed Consolidating Statements of Cash Flows
Year Ended December 31, 2011
(In thousands)

	Parent Company	Issuer	Guarantor Subsidiaries	Non-Guarantor Subsidiaries	Consolidated


Cash provided by (used in) operating activities	$ (5,865)	$ –	$ 370,878	$ 100,232	$ 465,245
Investing Activities
Capital expenditures	–	–	(128,008)	(46,572)	(174,580)
Change in receivable from Arch Coal	(235,578)	–	–	927	(234,651)
Proceeds from dispositions of property, plant and equipment	–	–	85	71	156
Additions to prepaid royalties	–	–	(3,772)	(202)	(3,974)
Cash used in investing activities	(235,578)	–	(131,695)	(45,776)	(413,049)
Financing Activities
Net repayments on commercial paper	(56,904)	–	–	–	(56,904)
Debt financing costs	–	(16)	–	–	(16)
Transactions with affiliates, net	296,734	16	(242,195)	(54,555)	–
Cash provided by (used in) financing activities	239,830	–	(242,195)	(54,555)	(56,920)
Decrease in cash and cash equivalents	(1,613)	–	(3,012)	(99)	(4,724)
Cash and cash equivalents, beginning of period	1,613	–	78,070	134	79,817
Cash and cash equivalents, end of period	$ –	$ –	$ 75,058	$ 35	$ 75,093

Condensed Consolidating Statements of Cash Flows
Year Ended December 31, 2010
(In thousands)

	Parent Company	Issuer	Guarantor Subsidiaries	Non-Guarantor Subsidiaries	Consolidated

Cash provided by (used in) operating activities	$ (40,833)	$ (17,626)	$ 418,073	$ 78,762	$ 438,376
Investing Activities
Capital expenditures	–	–	(78,719)	(23,893)	(102,612)
Change in receivable from Arch Coal	3,083	–	–	9,720	12,803
Proceeds from dispositions of property, plant and equipment	–	–	50	29	79
Additions to prepaid royalties	–	–	(2,509)	(465)	(2,974)
Cash provided by (used in) investing activities	3,083	–	(81,178)	(14,609)	(92,704)
Financing Activities
Payments to retire debt	–	(505,627)	–	–	(505,627)
Loan from Arch Coal	225,000	–	–	–	225,000
Net proceeds from commercial paper	7,452	–	–	–	7,452
Debt financing costs	(375)	(15)	–	–	(390)
Contribution from redeemable membership interest	891	–	–	–	891
Transactions with affiliates, net	(200,319)	523,268	(258,886)	(64,063)	–
Cash provided by (used in) financing activities	32,649	17,626	(258,886)	(64,063)	(272,674)
Increase (decrease) in cash and cash equivalents	(5,101)	–	78,009	90	72,998
Cash and cash equivalents, beginning of period	6,714	–	61	44	6,819
Cash and cash equivalents, end of period	$ 1,613	$ –	$ 78,070	$ 134	$ 79,817

Condensed Consolidating Statements of Cash Flows
Year Ended December 31, 2009
(In thousands)

	Parent Company	Issuer	Guarantor Subsidiaries	Non-Guarantor Subsidiaries	Consolidated

Cash provided by (used in) operating activities	$ (95,111)	$ 824	$ 171,532	$ 100,874	$ 178,119
Investing Activities
Capital expenditures	–	–	(101,887)	(23,567)	(125,454)
Change in receivable from Arch Coal	(30,440)	–	–	(2,344)	(32,784)
Additions to prepaid royalties	–	–	(2,209)	(582)	(2,791)
Proceeds from dispositions of property, plant and equipment	–	–	66	25	91
Reimbursement of deposits on equipment	–	–	3,209	–	3,209
Cash used in investing activities	(30,440)	–	(100,821)	(26,468)	(157,729)
Financing Activities
Net repayments on commercial paper	(16,219)	–	–	–	(16,219)
Debt financing costs	(188)	(15)	–	–	(203)
Transactions with affiliates, net	145,982	(809)	(70,734)	(74,439)	–
Cash provided by (used in) financing activities	129,575	(824)	(70,734)	(74,439)	(16,422)
Increase (decrease) in cash and cash equivalents	4,024	–	(23)	(33)	3,968
Cash and cash equivalents, beginning of period	2,690	–	84	77	2,851
Cash and cash equivalents, end of period	$ 6,714	$ –	$ 61	$ 44	$ 6,819

Valuation and Qualifying Accounts

12 Months Ended

Dec. 31, 2011

Valuation and Qualifying Accounts [Abstract]

Schedule of Valuation and Qualifying Accounts

SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS

	Balance at Beginning of Year	Additions Charged to Costs and Expenses	Charged to Other Accounts	Deductions(a)	Balance at End of Year
	(In thousands)
Year Ended Dec. 31, 2011
Reserves deducted from asset accounts
Other assets — other notes and accounts receivable	$ —	$ —	$ —	$ —	$ —
Current assets — repair parts and supplies inventories	11,727	1,566	—	1,182	12,111
Year Ended Dec. 31, 2010
Reserves deducted from asset accounts
Other assets — other notes and accounts receivable	$ —	$ —	$ —	$ —	$ —
Current assets — repair parts and supplies inventories	12,583	1,774	—	2,630	11,727
Year Ended Dec. 31, 2009
Reserves deducted from asset accounts
Other assets — other notes and accounts receivable	$ —	$ —	$ —	$ —	$ —
Current assets — repair parts and supplies inventories	11,987	1,210	—	612	12,583

(a) Reserves utilized, unless otherwise indicated.

Charged to Costs

Balance at