Acquisitions (Details 2) (USD $)	12 Months Ended															3 Months Ended			12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Canadian and U.K. operations	Dec. 31, 2011 U.S. Operations	Dec. 31, 2010 U.S. Operations	Dec. 31, 2009 U.S. Operations	Dec. 31, 2011 Western Coal Corp	Dec. 31, 2010 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	Dec. 31, 2011 Western Coal Corp Canadian and U.K. operations	Dec. 31, 2011 Western Coal Corp U.S. Operations	Sep. 30, 2011 Western Coal Corp Preliminary	Sep. 30, 2011 Western Coal Corp Adjustments	Jun. 30, 2011 Western Coal Corp Adjustments	Dec. 31, 2011 Western Coal Corp Adjustments	Dec. 31, 2011 North River Mine M	May 06, 2011 North River Mine
Acquisitions
Depreciation and depletion	$ 245,509,000	$ 98,702,000	$ 72,939,000	$ 93,392,000	$ 151,341,000	$ 98,170,000	$ 72,533,000
Net income	349,176,000	385,797,000	137,158,000													4,100,000	7,800,000
Diluted net income per share (in dollars per share)	$ 5.76	$ 7.18	$ 2.55													$ 0.07	$ 0.13
Purchase consideration:
Cash consideration										2,173,080,000										1,100,000
Liabilities assumed																				90,900,000
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
Below-market coal sales contract liability																				70,000,000
Remaining maturity period of below-market coal sales contract liability (in months)																			26
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							122,012,000			(783,000)
Other current assets								86,475,000							65,606,000			20,869,000
Mineral interests								2,992,000,000							4,399,000,000			(1,407,000,000)
Property, plant and equipment								560,894,000							565,228,000			(4,334,000)
Goodwill								1,122,884,000					1,054,000,000	68,700,000	277,404,000			845,480,000	1,700,000
Other long-term assets								54,150,000							54,150,000
Total assets								5,135,365,000							5,681,133,000			(545,768,000)
Accounts payable and accrued liabilities								184,983,000							180,157,000			4,826,000
Other current liabilities								82,175,000							75,824,000			6,351,000
Deferred tax liability								1,021,161,000							1,576,896,000			(555,735,000)
Other long-term liabilities								100,844,000							102,054,000			(1,210,000)
Total liabilities								1,389,163,000							1,934,931,000			(545,768,000)
Net assets acquired								3,746,202,000							3,746,202,000
Acquisition related costs (included in Selling, general and administrative expenses at the end of the period)								23,200,000
Actual Western Coal Results Included in Walter Energy's Consolidated Results
Revenue								846,682,000
Net income								60,538,000
Supplemental Pro forma Combined Results
Revenue								2,795,566,000	2,358,040,000
Net income								$ 403,945,000	$ 325,196,000