Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Current assets
Cash and cash equivalents	$ 203,093	$ 379,680
Investments, at fair market value	259,014	261,983
Inventories	186,471	153,208
Trade receivables	14,303	9,953
Deferred income taxes	21,304	21,304
Other current assets	24,993	26,734
Total current assets	709,178	852,862
Mineral properties and mine development, net of $335,837 and $325,977 of accumulated depletion and amortization	914,416	899,225
Property, plant and equipment, net of $175,536 and $169,933 of accumulated depreciation	120,086	122,677
Deferred debt issuance costs	9,052	9,609
Other noncurrent assets	5,733	6,390
Total assets	1,758,465	1,890,763
Current liabilities
Accounts payable	37,548	28,623
Accrued compensation and benefits	30,597	31,369
Property, production and franchise taxes payable	12,487	13,722
Current portion of long-term debt and capital lease obligations	1,957	168,432
Income taxes payable	669	0
Other current liabilities	6,641	4,702
Total current liabilities	89,899	246,848
Long-term debt and capital lease obligations	298,194	292,685
Deferred income taxes	196,863	199,802
Accrued workers compensation	6,199	5,815
Asset retirement obligation	8,132	7,965
Other noncurrent liabilities	7,927	5,068
Total liabilities	607,214	758,183
Stockholders’ equity
Preferred stock, $0.01 par value, 1,000,000 shares authorized; none issued	0	0
Common stock, $0.01 par value, 200,000,000 shares authorized; 118,002,829 and 116,951,081 shares issued and outstanding	1,180	1,170
Paid-in capital	1,063,261	1,058,978
Accumulated earnings	35,353	20,770
Accumulated other comprehensive loss	(25)	(99)
Total stockholders’ equity	1,099,769	1,080,819
Noncontrolling interest	51,482	51,761
Total equity	1,151,251	1,132,580
Total liabilities and equity	$ 1,758,465	$ 1,890,763