CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (Cloud Peak Energy Inc. and Subsidiaries) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME
Revenue	$ 329,996	$ 343,183	$ 668,048	$ 716,086
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, and accretion, shown separately)	281,603	266,073	557,631	549,018
Depreciation and depletion	25,459	22,285	48,671	45,675
Accretion	4,126	3,422	8,253	6,070
Derivative mark-to-market gains	(12,284)	(20,183)	(25,936)	(18,127)
Selling, general and administrative expenses	12,834	12,556	26,442	27,298
Other operating costs	1,191	308	1,301	401
Total costs and expenses	312,929	284,461	616,362	610,335
Operating income	17,067	58,722	51,686	105,751
Other income (expense)
Interest income	63	312	188	758
Interest expense	(10,315)	(7,936)	(20,799)	(13,786)
Other, net	43	(111)	(198)	(53)
Total other expense	(10,209)	(7,735)	(20,809)	(13,081)
Income before income tax provision and earnings from unconsolidated affiliates	6,858	50,987	30,877	92,670
Income tax expense	(2,462)	(18,806)	(11,297)	(33,908)
Earnings from unconsolidated affiliates, net of tax	313	1,497	524	1,534
Net income	4,709	33,678	20,104	60,296
Other comprehensive income
Retiree medical plan amortization of prior service costs	444	394	888	788
Other postretirement plan adjustments			30	90
Income tax on retiree medical plan and pension adjustments	(160)	(142)	(330)	(316)
Other comprehensive income	284	252	588	562
Total comprehensive income	$ 4,993	$ 33,930	$ 20,692	$ 60,858
Income per common share:
Basic (in dollars per share)	$ 0.08	$ 0.56	$ 0.33	$ 1.00
Diluted (in dollars per share)	$ 0.08	$ 0.55	$ 0.33	$ 0.99
Weighted-average shares outstanding - basic (in shares)	60,629	60,015	60,619	60,011
Weighted-average shares outstanding - diluted (in shares)	61,165	60,870	61,123	60,826