Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Current assets
Cash and cash equivalents	$ 171,724	$ 147,336
Investments, at fair value (Note 11)	280,658	316,429
Inventories	105,185	102,072
Trade receivables	1,223	800
Prepaid expenses	1,295	2,821
Other current assets	26,617	21,628
Total current assets	586,702	591,086
Mineral properties	112,480	112,480
Mine development, net	467,285	460,751
Property, plant and equipment, net	104,630	109,957
Other noncurrent assets	4,142	4,115
Total assets	1,275,239	1,278,389
Current liabilities
Accounts payable	17,779	18,205
Accrued compensation and benefits	28,646	30,046
Property, production and franchise taxes payable	12,676	13,907
Current portion of long-term debt and capital lease obligations	46	657
Other current liabilities	6,768	5,286
Total current liabilities	65,915	68,101
Long-term debt and capital lease obligations	259,661	255,099
Deferred income taxes	22,235	22,761
Accrued workers compensation	6,347	6,070
Asset retirement obligation	10,947	11,027
Other noncurrent liabilities	9,826	6,102
Total liabilities	374,931	369,160
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; 121,072,613 and 121,049,471 issued and outstanding at March 31, 2016 and December 31, 2015, respectively	1,211	1,210
Paid-in capital	1,099,944	1,099,283
Accumulated deficit	(200,997)	(191,067)
Accumulated other comprehensive income (loss)	150	(197)
Total stockholders’ equity	900,308	909,229
Total liabilities and equity	$ 1,275,239	$ 1,278,389