Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities:
Net income	$ 8,240	$ 26,834
Non-cash elements included in net income:
Depreciation, depletion and amortization	29,490	29,590
Unrealized (gain) on investments	(310)	(327)
Loss on disposal of investments		167
Gain on disposition of properties, plants, equipment, and mineral interests	(129)	(32)
Provision for reclamation and closure costs	1,323	1,026
Stock compensation	1,127	1,349
Deferred income taxes	(438)	(21,234)
Amortization of loan origination fees	449	480
(Gain) loss on derivative contracts	(9,094)	7,343
Foreign exchange (gain) loss	(3,399)	506
Other non-cash items, net	(36)	2
Change in assets and liabilities:
Accounts receivable	(7,266)	(8,738)
Inventories	(6,762)	(3,358)
Other current and non-current assets	(3,171)	1,363
Accounts payable and accrued liabilities	13,956	(1,510)
Accrued payroll and related benefits	(3,927)	6,881
Accrued taxes	218	1,754
Accrued reclamation and closure costs and other non-current liabilities	(3,888)	(3,811)
Cash provided by operating activities	16,383	38,285
Investing activities:
Additions to properties, plants, equipment and mineral interests	(17,635)	(21,658)
Proceeds from disposition of properties, plants and equipment	151	61
Purchases of investments	(31,182)	(11,113)
Maturities of investments	30,501	3,634
Net cash used in investing activities	(18,165)	(29,076)
Financing activities:
Acquisition of treasury shares	(1,225)	(731)
Dividends paid to common stockholders	(998)	(989)
Dividends paid to preferred stockholders	(138)	(138)
Credit facility fees paid		(91)
Borrowings on debt	31,024
Repayments of debt		(470)
Repayments of capital leases	(1,322)	(1,595)
Net cash provided by (used in) financing activities	27,341	(4,014)
Effect of exchange rates on cash	876	1,814
Net increase in cash, cash equivalents and restricted cash and cash equivalents	26,435	7,009
Cash, cash equivalents and restricted cash and cash equivalents at beginning of period	187,139	171,977
Cash, cash equivalents and restricted cash and cash equivalents at end of period	213,574	178,986
Significant non-cash investing and financing activities:
Addition of capital lease obligations	2,446	1,798
Payment of accrued compensation in stock	$ 4,863	$ 4,240