Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Current assets
Cash and cash equivalents	$ 130,115	$ 147,336
Investments	312,037	316,429
Inventories	113,892	102,072
Trade receivables	890	800
Prepaid expenses	5,660	2,821
Other current assets	25,505	21,628
Total current assets	588,099	591,086
Mineral properties	112,480	112,480
Mine development, net	473,383	460,751
Property, plant and equipment, net	102,337	109,957
Other noncurrent assets	4,932	4,115
Total assets	1,281,231	1,278,389
Current liabilities
Accounts payable	22,304	18,205
Accrued compensation and benefits	28,195	30,046
Property, production and franchise taxes payable	13,617	13,907
Current portion of long-term debt and capital lease obligations	0	657
Income taxes payable	373	0
Other current liabilities	4,369	5,286
Total current liabilities	68,858	68,101
Long-term debt	264,301	255,099
Deferred income taxes	20,310	22,761
Accrued workers compensation	6,479	6,070
Asset retirement obligation	11,159	11,027
Other noncurrent liabilities	7,845	6,102
Total liabilities	378,952	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; 121,074,473 and 121,049,471 issued and outstanding at June 30, 2016 and December 31, 2015, respectively	1,211	1,210
Paid-in capital	1,100,949	1,099,283
Accumulated deficit	(200,213)	(191,067)
Accumulated other comprehensive income (loss)	332	(197)
Total stockholders’ equity	902,279	909,229
Total liabilities and equity	$ 1,281,231	$ 1,278,389