Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
OPERATING ACTIVITIES
Net income	$ 142,840	$ 159,394	$ 42,179
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation, depletion and amortization	466,587	365,066	301,608
Amortization of acquired sales contracts, net	(22,069)	35,606	19,623
Bridge financing costs related to ICG	49,490
Write down of assets acquired from ICG	7,316
Prepaid royalties expensed	34,842	34,605	29,746
Employee stock-based compensation	10,882	11,717	13,394
Amortization relating to financing activities	14,067	10,398	6,741
Gain on Knight Hawk transaction		(41,577)
Net loss resulting from early retirement of debt	1,958	6,776
Changes in operating assets and liabilities:
Receivables	(74,914)	(7,287)	47,794
Inventories	(50,900)	5,160	(28,518)
Coal derivative assets and liabilities	6,079	9,554	32,266
Accounts payable, accrued expenses and other current liabilities	52,191	87,807	(44,764)
Income tax payable/receivable	(21,759)	(1,364)	2,100
Deferred income taxes	10,519	(12,405)	(34,668)
Asset retirement obligations	3,868	23,997	18,741
Other	11,245	9,700	(23,262)
Cash provided by operating activities	642,242	697,147	382,980
INVESTING ACTIVITIES
Acquisitions of businesses, net of cash acquired	(2,894,339)		(768,819)
Increase in restricted cash	5,167
Capital expenditures	(540,936)	(314,657)	(323,150)
Proceeds from dispositions of property, plant and equipment	25,887	330	825
Additions to prepaid royalties	(29,957)	(27,355)	(26,755)
Purchases of investments and advances to affiliates	(61,909)	(46,185)	(10,925)
Consideration paid related to prior business acquisitions	(829)	(1,262)	(4,767)
Reimbursement of deposits on equipment			3,209
Cash used in investing activities	(3,496,916)	(389,129)	(1,130,382)
FINANCING ACTIVITIES
Proceeds from the issuance of senior notes	2,000,000	500,000	584,784
Proceeds from the issuance of common stock, net	1,267,933		326,452
Payments to retire debt	(605,178)	(505,627)
Net increase (decrease) in borrowings under lines of credit and commercial paper program	424,396	(196,549)	(85,815)
Net proceeds from (payments on) other debt	5,334	82	(2,986)
Debt financing costs	(114,823)	(12,751)	(29,659)
Dividends paid	(80,748)	(63,373)	(54,969)
Issuance of common stock under incentive plans	2,316	1,764	84
Contribution from noncontrolling interest		891
Cash provided by (used in) financing activities	2,899,230	(275,563)	737,891
Increase (decrease) in cash and cash equivalents	44,556	32,455	(9,511)
Cash and cash equivalents, beginning of year	93,593	61,138	70,649
Cash and cash equivalents, end of year	138,149	93,593	61,138
SUPPLEMENTAL CASH FLOW INFORMATION:
Cash paid during the year for interest	213,697	134,866	76,801
Cash paid during the year for income taxes	$ 7,094	$ 36,765	$ 17,482