Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES
Net (loss) income	$ (9,930)	$ 22,888
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Depletion, depreciation and amortization	17,260	17,121
Loss on long-term investments	0	55
Amortization / accretion on investment premium / discount	607	420
(Gain) loss on disposal of property, plant and equipment	(1)	3
Foreign currency transaction (gain) loss, net	(1,192)	608
Deferred income taxes	355	(12,409)
Accretion of asset retirement obligation	208	191
Amortization of deferred debt issuance costs	217	303
Accretion of convertible debenture debt discount	4,345	4,525
Share based compensation and other benefits	732	3,438
Non-cash capitalized interest	(1,292)	(866)
Changes in operating assets and liabilities:
Inventories	(2,057)	5,997
Trade receivables	(423)	125
Prepaid expenses	1,526	1,183
Accrued compensation and benefits	(1,400)	(2,152)
Accounts payable	(83)	(2,043)
Property, production and franchise taxes payable	2,494	794
Accrued workers compensation	277	(146)
Other operating assets	(4,879)	(1,879)
Other operating liabilities	1,357	156
NET CASH PROVIDED BY OPERATING ACTIVITIES	8,121	38,312
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures	(18,842)	(27,902)
Proceeds from disposal of property, plant and equipment	1	0
Purchases of investments	(75,531)	(57,371)
Proceeds from maturities and sales of investments	111,250	29,839
NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES	16,878	(55,434)
CASH FLOWS FROM FINANCING ACTIVITIES
Payments on debt and capital lease obligations	(612)	(584)
Proceeds from issuance of common stock	1	28
NET CASH USED IN FINANCING ACTIVITIES	(611)	(556)
CASH AND CASH EQUIVALENTS
Net increase (decrease)	24,388	(17,678)
Balance at beginning of period	147,336	280,286
BALANCE AT END OF PERIOD	$ 171,724	$ 262,608