CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Cloud Peak Energy Inc. and Subsidiaries) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Cash flows from operating activities
Net income	$ 20,104	$ 60,296
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and depletion	48,671	45,675
Accretion	8,253	6,070
Earnings from unconsolidated affiliates	(524)	(1,534)
Distributions of income from unconsolidated affiliates	2,000
Deferred income taxes	10,114	23,679
Stock compensation expense	3,747	6,371
Derivative mark-to-market gains	(25,936)	(18,127)
Other	6,879	5,812
Changes in operating assets and liabilities:
Accounts receivable	(19,909)	4,038
Inventories, net	(833)	(6,171)
Due to or from related parties	725	28
Other assets	(10,587)	(13,225)
Accounts payable and accrued expenses	(371)	(29,214)
Asset retirement obligations	(555)	(2,940)
Cash received for financial derivative instruments	2,529	524
Net cash provided by operating activities	44,307	81,282
Investing activities
Acquisition of Youngs Creek and CX Ranch coal and land assets		(300,259)
Purchases of property, plant and equipment	(24,475)	(21,875)
Cash paid for capitalized interest	(8,263)	(36,477)
Investments in marketable securities	(32,961)	(53,854)
Maturity and redemption of investments	32,801	28,887
Investment in project development	(4,087)
Return of restricted cash		71,244
Partnership escrow deposit		(4,470)
Return of partnership escrow	4,468
Other	63	1,825
Net cash used in investing activities	(32,454)	(314,979)
Financing activities
Principal payments on federal coal leases	(8,852)	(48,959)
Payment of deferred financing fees	(865)
Other	(80)
Net cash used in financing activities	(9,797)	(48,959)
Net increase (decrease) in cash and cash equivalents	2,056	(282,656)
Cash and cash equivalents at beginning of period	197,691	404,240
Cash and cash equivalents at end of period	199,747	121,584
Supplemental cash flow disclosures:
Interest paid	27,259	46,616
Income taxes paid	10,377	20,788
Supplemental noncash investing and financing activities:
Non-cash interest capitalized	8,240	9,635
Capital expenditures included in accounts payable	7,194	4,363
Assets acquired under capital leases	$ 7,601