Acquisition (Details)			1 Months Ended				3 Months Ended		9 Months Ended					1 Months Ended
	Sep. 30, 2011 USD ($)	Apr. 02, 2011 USD ($)	Apr. 30, 2011 Western Coal Corporation USD ($)	Jan. 31, 2011 Western Coal Corporation USD ($)	Dec. 31, 2010 Western Coal Corporation	Nov. 30, 2010 Western Coal Corporation count	Sep. 30, 2011 Western Coal Corporation USD ($)	Sep. 30, 2010 Western Coal Corporation USD ($)	Sep. 30, 2011 Western Coal Corporation USD ($)	Sep. 30, 2010 Western Coal Corporation USD ($)	Apr. 02, 2011 Western Coal Corporation USD ($)	Dec. 02, 2010 Western Coal Corporation CAD	Nov. 17, 2010 Western Coal Corporation CAD	May 31, 2011 Chevron Mining, Inc M	May 06, 2011 Chevron Mining, Inc USD ($)	May 06, 2011 Chevron Mining, Inc U.S. Operations USD ($)	Sep. 30, 2011 Canadian and U.K. operations USD ($)	Sep. 30, 2011 U.S. Operations USD ($)	Apr. 02, 2011 2011 Credit Agreement USD ($)
Acquisitions
Common shares to be purchased under share purchase agreement						54,500,000
Percentage of outstanding shares to be acquired under the share purchase agreement													19.80%
Acquisition price per share of common stock under the share purchase agreement (in dollars per share)													11.50
Acquisition price per share of common stock under the arrangement agreement (in dollars per share)												11.50
Number of separate transactions						2
Number of the entity's shares of common stock offered for exchange under the arrangement agreement					0.114
Common shares purchased under share purchase agreement				25,274,745
Percentage of outstanding shares acquired				9.15%
Cash paid for common shares purchased				$ 293,700,000			$ 2,432,693,000		$ 2,432,693,000		$ 2,173,080,000				$ 1,100,000
Gain on remeasurement of previously held noncontrolling interest			20,500,000
Number of shares issued to acquired entity			8,951,558
Value of common shares issued to acquire the entity											1,200,000,000
Fair value of company's common stock (in dollars per share)		$ 136.75
Stock options issued in exchange of outstanding stock options (in shares)			193,498
Fair value of stock options issued			15,500,000
Walter Credit Agreement
Maximum amount of borrowings available under the credit agreement																			2,725,000,000
Purchase consideration:
Cash consideration				293,700,000			2,432,693,000		2,432,693,000		2,173,080,000				1,100,000
Fair value of shares of common stock issued											1,224,126,000
Fair value of stock options issued and warrants											34,765,000
Fair value of consideration transferred											3,431,971,000
Fair value of equity interest at date of acquisition											314,231,000
Total consideration											3,746,202,000
Fair value of assets acquired and liabilities assumed:
Cash and cash equivalents											34,065,000
Receivables											163,668,000
Inventories											122,012,000
Other current assets											65,606,000
Mineral interests											4,399,000,000
Property, plant and equipment											565,228,000
Goodwill	278,425,000										277,404,000					1,600,000
Other long-term assets											54,150,000
Total assets							5,681,133,000		5,681,133,000		5,681,133,000
Accounts payable and accrued liabilities											180,157,000
Other current liabilities											75,824,000
Deferred tax liability											1,576,896,000
Other long-term liabilities											102,054,000
Total liabilities							1,934,931,000		1,934,931,000		1,934,931,000				90,900,000
Below-market coal sales contract liability															70,000,000
Remaining maturity period of below-market coal sales contract liability (in months)														29
Net assets acquired											3,746,202,000
Amount of increase in goodwill							27,400,000
Amount of goodwill allocated based on purchase price allocation																	253,300,000	24,100,000
Acquisition related costs (included in Selling, general and administrative expenses at the end of the period)							6,100,000		23,100,000
Actual Western Coal Results Included in Walter Energy's Consolidated Results
Revenue							270,295,000		576,660,000
Net income							34,684,000		42,163,000
Supplemental Pro forma Combined Results
Revenue							690,069,000	698,886,000	2,096,011,000	1,749,965,000
Net income							$ 74,417,000	$ 141,669,000	$ 306,643,000	$ 251,397,000