Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Current assets
Cash and cash equivalents	$ 262,608	$ 280,286
Investments, at fair market value	278,565	251,254
Inventories	123,372	130,307
Trade receivables	1,152	1,277
Deferred income taxes	17,800	21,055
Prepaids	1,363	2,546
Other current assets	15,123	14,671
Total current assets	699,983	701,396
Mineral properties	159,252	159,252
Mine development, net	422,551	409,754
Property, plant and equipment, net	115,957	118,881
Deferred debt issuance costs	5,729	6,032
Other noncurrent assets	5,571	4,012
Total assets	1,409,043	1,399,327
Current liabilities
Accounts payable	22,535	26,806
Accrued compensation and benefits	27,821	29,973
Property, production and franchise taxes payable	13,787	15,828
Current portion of long-term debt and capital lease obligations	2,172	2,144
Other current liabilities	8,561	7,288
Total current liabilities	74,876	82,039
Long-term debt and capital lease obligations	297,933	294,023
Deferred income taxes	52,798	68,896
Accrued workers compensation	5,914	6,060
Asset retirement obligation	9,292	9,401
Other noncurrent liabilities	10,035	7,200
Total liabilities	450,848	467,619
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; 120,619,315 and 120,381,746 shares issued and outstanding	1,206	1,204
Paid-in capital	1,094,607	1,091,146
Accumulated deficit	(156,136)	(179,139)
Accumulated other comprehensive income	153	17
Total stockholders’ equity	939,830	913,228
Noncontrolling interest	18,365	18,480
Total equity	958,195	931,708
Total liabilities and equity	$ 1,409,043	$ 1,399,327