Acquisitions (Details 2) (USD $)	3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended			3 Months Ended	9 Months Ended		3 Months Ended	9 Months Ended								3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Canadian and U.K. operations	Sep. 30, 2011 Canadian and U.K. operations	Sep. 30, 2012 Canadian and U.K. operations	Sep. 30, 2011 Canadian and U.K. operations	Dec. 31, 2011 Canadian and U.K. operations	Sep. 30, 2012 U.S. Operations	Sep. 30, 2011 U.S. Operations	Sep. 30, 2012 U.S. Operations	Sep. 30, 2011 U.S. Operations	Dec. 31, 2011 U.S. Operations	Sep. 30, 2011 Previously reported/Preliminary	Sep. 30, 2011 Previously reported/Preliminary	Dec. 31, 2011 Previously reported/Preliminary	Sep. 30, 2011 Western Coal Corp	Sep. 30, 2011 Western Coal Corp	Mar. 31, 2012 Western Coal Corp	Apr. 02, 2011 Western Coal Corp	Apr. 02, 2011 Western Coal Corp Common stock of Walter Energy	Apr. 02, 2011 Western Coal Corp Stock options issued and warrants assumed	Sep. 30, 2012 Western Coal Corp Canadian and U.K. operations	Sep. 30, 2012 Western Coal Corp U.S. Operations	Dec. 31, 2011 Western Coal Corp Previously reported/Preliminary	Sep. 30, 2011 Western Coal Corp Adjustments Purchase price allocation adjustments	Sep. 30, 2011 Western Coal Corp Adjustments Purchase price allocation adjustments	Dec. 31, 2011 Western Coal Corp Adjustments Purchase price allocation adjustments	Sep. 30, 2012 Western Coal Corp Adjustments Purchase price allocation adjustments
Acquisitions
Net income (loss)	$ (1,061,956,000)	$ 87,080,000	$ (989,404,000)	$ 283,346,000												$ 76,221,000	$ 265,392,000											$ 10,900,000	$ 18,000,000	$ 14,400,000
ASSETS
Inventories	374,239,000		374,239,000		240,437,000													242,607,000
Other current assets	22,096,000		22,096,000		45,649,000													45,627,000
Mineral interests, net	2,980,924,000		2,980,924,000		3,056,258,000													2,946,113,000
Property, plant and equipment, net	1,720,137,000		1,720,137,000		1,631,333,000													1,637,182,000
Goodwill					1,066,754,000					992,434,000					74,320,000			1,124,597,000
LIABILITIES AND STOCKHOLDERS' EQUITY
Other current liabilities	42,188,000		42,188,000		63,757,000													59,827,000
Deferred income taxes	951,835,000		951,835,000		1,029,336,000													1,003,383,000
Retained earnings	(268,664,000)		(268,664,000)		744,939,000													730,517,000
Company's recast and previously reported condensed consolidated statements of operations
Sales	612,510,000	683,730,000	1,908,413,000	1,854,892,000												685,052,000	1,858,343,000
Cost of sales (exclusive of depreciation and depletion)	448,765,000	420,690,000	1,366,383,000	1,105,224,000												425,487,000	1,106,008,000
Depreciation and depletion	82,560,000	57,144,000	223,512,000	157,972,000		37,305,000	13,408,000	91,976,000	46,651,000		44,789,000	43,546,000	130,635,000	110,750,000		63,046,000	180,830,000
Operating income	(1,071,765,000)	158,027,000	(919,716,000)	442,257,000		(1,036,690,000)	52,361,000	(1,074,924,000)	71,161,000		(22,228,000)	120,078,000	191,998,000	432,184,000		148,650,000	422,066,000
Income before income tax expense	(1,103,140,000)	117,282,000	(1,022,556,000)	390,728,000												107,905,000	370,537,000
Income tax expense (benefit)	(41,184,000)	30,202,000	(27,972,000)	107,382,000												31,684,000	105,145,000
Net income (loss)	(1,061,956,000)	87,080,000	(989,404,000)	283,346,000												76,221,000	265,392,000											10,900,000	18,000,000	14,400,000
Net income per share:
Basic (in dollars per share)	$ (16.97)	$ 1.40	$ (15.82)	$ 4.75												$ 1.22	$ 4.45
Diluted (in dollars per share)	$ (16.97)	$ 1.39	$ (15.82)	$ 4.72												$ 1.21	$ 4.43
Company's recast and previously reported condensed consolidated statements of cash flows
Net income (loss)	(1,061,956,000)	87,080,000	(989,404,000)	283,346,000												76,221,000	265,392,000											10,900,000	18,000,000	14,400,000
Adjustments to reconcile net income (loss) from continuing operations to net cash flows provided by (used in) operating activities:
Depreciation and depletion	82,560,000	57,144,000	223,512,000	157,972,000		37,305,000	13,408,000	91,976,000	46,651,000		44,789,000	43,546,000	130,635,000	110,750,000		63,046,000	180,830,000
Deferred income tax credit			(100,419,000)	(16,901,000)													(19,138,000)
Other			41,022,000	8,349,000													29,098,000
Decrease in current assets, net of effect of business acquisitions:
Inventories			(113,601,000)	21,856,000													(1,560,000)
Purchase consideration:
Cash consideration																						2,173,080,000
Fair value of shares of common stock issued or stock options issued and warrants																							1,224,126,000	34,765,000
Fair value of consideration transferred																						3,431,971,000
Business Combination Step Acquisition Equity Interest in Acquiree Fair Value																						314,231,000
Total consideration																						3,746,202,000
Fair value of assets acquired and liabilities assumed
Cash and cash equivalents																					34,065,000						34,065,000
Receivables																					163,668,000						163,668,000
Inventories																					121,229,000						121,229,000
Other current assets																					86,498,000						86,475,000				23,000
Mineral interests																					3,086,000,000						2,992,000,000				94,000,000
Property, plant and equipment																					554,192,000						560,894,000				(6,702,000)
Goodwill																					1,065,040,000				992,400,000	72,600,000	1,122,884,000				(57,844,000)
Other long-term assets																					54,150,000						54,150,000
Total assets																					5,164,842,000						5,135,365,000				29,477,000
Accounts payable and accrued liabilities																					184,983,000						184,983,000
Other current liabilities																					86,105,000						82,175,000				3,930,000
Deferred tax liability																					1,046,708,000						1,021,161,000				25,547,000
Other long-term liabilities																					100,844,000						100,844,000
Total liabilities																					1,418,640,000						1,389,163,000				29,477,000
Net assets acquired																					3,746,202,000						3,746,202,000
Acquisition and integration related costs (included in Selling, general and administrative expenses at the end of the period)																			6,100,000	23,100,000
Supplemental Pro forma Combined Results
Revenue																				2,092,560,000
Net income																				$ 338,106,000