CONSOLIDATED BALANCE SHEETS (Cloud Peak Energy Inc. and Subsidiaries) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Current assets
Cash and cash equivalents	$ 404,240	$ 340,101
Restricted cash	71,245	182,072
Investments in marketable securities	75,228
Accounts receivable, net	95,247	65,173
Due from related parties	471	434
Inventories	71,648	64,970
Deferred income taxes	37,528	21,552
Other assets	15,294	17,449
Total current assets	770,901	691,751
Noncurrent assets
Property, plant and equipment, net	1,350,135	1,008,337
Goodwill	35,634	35,634
Deferred income taxes	132,828	140,985
Other assets	29,821	38,400
Total assets	2,319,319	1,915,107
Current liabilities
Accounts payable	71,427	81,975
Royalties and production taxes	136,072	127,038
Accrued expenses	65,928	51,197
Current portion of tax agreement liability	19,113	18,226
Current portion of federal coal lease obligations	102,198	54,630
Other liabilities	4,971	4,880
Total current liabilities	399,709	337,946
Noncurrent liabilities
Tax agreement liability, net of current portion	151,523	171,885
Senior notes	596,077	595,684
Federal coal lease obligations, net of current portion	186,119	63,659
Asset retirement obligations, net of current portion	192,707	182,170
Other liabilities	42,795	32,564
Total liabilities	1,568,930	1,383,908
Commitments and Contingencies (Note 15)
Equity
Common stock ($0.01 par value; 200,000 shares authorized; 60,923 and 60,878 shares issued and outstanding at December 31, 2011 and December 31, 2010, respectively)	609	609
Additional paid-in capital	536,301	502,952
Retained earnings	232,093	42,296
Accumulated other comprehensive loss	(18,614)	(14,658)
Total equity	750,389	531,199
Total liabilities and equity	$ 2,319,319	$ 1,915,107