CONSOLIDATED BALANCE SHEETS (Cloud Peak Energy Inc. and Subsidiaries) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Current assets
Cash and cash equivalents	$ 197,691	$ 404,240
Investments in marketable securities	80,341	75,228
Restricted cash		71,245
Accounts receivable	76,117	95,247
Due from related parties	1,561	471
Inventories, net	81,675	71,648
Deferred income taxes	28,112	37,528
Derivative financial instruments	13,785	2,275
Other assets	16,513	13,019
Total current assets	495,795	770,901
Noncurrent assets
Property, plant and equipment, net	1,678,294	1,350,135
Goodwill	35,634	35,634
Deferred income taxes	101,075	132,828
Other assets	40,525	29,821
Total assets	2,351,323	2,319,319
Current liabilities
Accounts payable	49,589	71,427
Royalties and production taxes	129,351	136,072
Accrued expenses	50,364	65,928
Current portion of tax agreement liability	19,485	19,113
Current portion of federal coal lease obligations	63,191	102,198
Other liabilities	2,770	4,971
Total current liabilities	314,750	399,709
Noncurrent liabilities
Tax agreement liability, net of current portion	97,053	151,523
Senior notes	596,506	596,077
Federal coal lease obligations, net of current portion	122,928	186,119
Asset retirement obligations, net of current portion	238,991	192,707
Other liabilities	50,073	42,795
Total liabilities	1,420,301	1,568,930
Commitments and Contingencies (Note 15)
Equity
Common stock ($0.01 par value; 200,000 shares authorized; 61,114 and 60,923 shares issued and 60,839 and 60,923 outstanding at December 31, 2012 and 2011, respectively)	608	609
Treasury stock 276 shares and 0 shares at December 31, 2012 and 2011, respectively	(5,390)
Additional paid-in capital	550,452	536,301
Retained earnings	405,813	232,093
Accumulated other comprehensive loss	(20,461)	(18,614)
Total equity	931,022	750,389
Total liabilities and equity	$ 2,351,323	$ 2,319,319