Condensed Consolidated Statements Of Cash Flows (USD $) In Thousands	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
OPERATING ACTIVITIES
Net income	$ 67,271	$ 64,504
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation, depletion and amortization	178,720	176,278
Amortization of acquired sales contracts, net	7,433	15,967
Bridge financing costs related to ICG	49,490
Net loss resulting from early retirement of ICG debt	250
Write down of assets acquired from ICG	7,316
Prepaid royalties expensed	19,491	16,048
Employee stock-based compensation expense	7,071	7,439
Amortization of debt financing costs	5,093	4,901
Gain on Knight Hawk transaction		(41,577)
Changes in:
Receivables	(25,329)	(44,057)
Inventories	(37,113)	2,458
Coal derivative assets and liabilities	4,902	11,631
Accounts payable, accrued expenses and other current liabilities	8,912	32,060
Income taxes, net	(15,186)	(309)
Deferred income taxes	20,873	(4,719)
Other	15,006	18,731
Cash provided by operating activities	314,200	259,355
INVESTING ACTIVITIES
Acquisition of ICG, net of cash acquired	(2,910,380)
Change in restricted cash	(74,814)
Capital expenditures	(107,725)	(171,958)
Proceeds from dispositions of property, plant and equipment	1,411	229
Purchases of investments and advances to affiliates	(38,059)	(14,249)
Additions to prepaid royalties	(25,212)	(23,466)
Cash used in investing activities	(3,154,779)	(209,444)
FINANCING ACTIVITIES
Proceeds from the issuance of senior notes	2,000,000
Proceeds from the issuance of common stock, net	1,249,407
Payments to retire ICG debt	(307,984)
Increase in restricted cash for retirement of ICG debt	(260,663)
Net increase (decrease) in borrowings under lines of credit and commercial paper program	303,096	(15,555)
Net payments on other debt	(8,845)	(8,249)
Debt financing costs	(112,334)	(437)
Dividends paid	(34,192)	(30,870)
Issuance of common stock under incentive plans	846	137
Contribution from noncontrolling interest		891
Cash provided by (used in) financing activities	2,829,331	(54,083)
Decrease in cash and cash equivalents	(11,248)	(4,172)
Cash and cash equivalents, beginning of period	93,593	61,138
Cash and cash equivalents, end of period	$ 82,345	$ 56,966