CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Cloud Peak Energy Inc. and Subsidiaries) (USD $) In Thousands	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Cash flows from operating activities
Net income	$ 145,978	$ 87,448
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and depletion	58,537	75,212
Amortization		3,197
Accretion	9,420	9,903
Earnings from unconsolidated affiliates	(2,142)	(2,499)
Distributions of income from unconsolidated affiliates	2,000	15
Deferred income taxes	(9,781)	21,330
Tax agreement expense	19,855	19,669
Stock compensation expense	6,315	5,379
Other, net	8,920	2,850
Changes in operating assets and liabilities:
Accounts receivable, net	(32,289)	(4,733)
Inventories	(7,561)	(2,445)
Due to or from related parties	(948)	5,442
Other assets	(4,539)	(7,762)
Accounts payable and accrued expenses	23,561	51,837
Asset retirement obligations	(4,851)	(4,005)
Net cash provided by operating activities	212,475	260,838
Investing activities
Purchases of property, plant and equipment	(100,822)	(56,129)
Initial payment on federal coal leases	(69,407)
Return of restricted cash	107,887	80,180
Restricted cash deposit		(218,397)
Other	545	1,469
Net cash used in investing activities	(61,797)	(192,877)
Financing activities
Principal payments on federal coal leases	(50,902)	(47,276)
Distributions to Rio Tinto		(1,288)
Other	(2,317)
Net cash used in financing activities	(53,219)	(48,564)
Net increase (decrease) in cash and cash equivalents	97,459	19,397
Cash and cash equivalents at beginning of period	340,101	268,316
Cash and cash equivalents at end of period	$ 437,560	$ 287,713