Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities:
Net income (loss)	$ (99,557)	$ (26,563)	$ (28,520)
Non-cash elements included in net loss:
Depreciation, depletion and amortization	204,475	140,905	126,467
Loss on disposition of investments	(923)	34	166
Unrealized loss on investments	2,386	2,816	251
Adjustment of inventory to market value	1,399	8,191	0
Fee on prepayment of debt with shares of common stock	2,855	0	0
Loss (gain) on disposition of properties, plants, equipment and mineral interests	4,643	(2,793)	(6,042)
Provision for reclamation and closure costs	6,914	6,090	4,508
Deferred income taxes	(33,387)	(9,699)	19,392
Stock compensation	5,668	6,278	6,323
Amortization of loan origination fees	2,637	2,077	1,864
Loss (gain) on derivative contracts	5,613	(15,366)	20,741
Foreign exchange loss (gain)	8,025	(7,104)	10,208
Other non-cash items	45	(66)	52
Change in assets and liabilities, net of business acquired:
Accounts receivable	(10,939)	9,843	(2,414)
Inventories	16,146	(27,512)	(3,744)
Other current and non-current assets	15,618	(1,726)	(11,595)
Accounts payable and accrued liabilities	(24,355)	17,795	(16,434)
Accrued payroll and related benefits	9,226	(2,425)	2,092
Accrued taxes	(3,155)	645	(2,234)
Accrued reclamation and closure costs and other non-current liabilities	7,532	(7,199)	(5,203)
Net cash provided by operating activities	120,866	94,221	115,878
Investing activities:
Additions to properties, plants, equipment and mineral interests	(121,421)	(136,933)	(98,038)
Proceeds from sale of investments	1,760	0	0
Proceeds from disposition of properties, plants and equipment	183	2,411	374
Insurance proceeds received for damaged property	0	4,377	7,745
Purchases of investments	(389)	(31,971)	(56,613)
Maturities of investments	0	64,895	49,969
Purchase of other companies, net of cash and restricted cash acquired	0	(139,326)	0
Net cash used in investing activities	(119,867)	(236,547)	(96,563)
Financing activities:
Proceeds from issuance of common stock, net of offering costs	49,019	6,744	9,610
Dividends paid to common stockholders	(4,914)	(4,393)	(3,976)
Dividend paid to preferred stockholders	(552)	(552)	(552)
Debt issuance and credit facility fees paid	(976)	(2,638)	(476)
Acquisition of treasury shares from employee equity awards	(2,231)	(2,694)	(2,868)
Borrowings on debt	279,500	102,024	0
Repayments of debt	(279,500)	(106,036)	(470)
Repayments of finance leases	(7,157)	(7,339)	(6,516)
Net cash provided by (used in) financing activities	33,189	(14,884)	(5,248)
Effect of exchange rates on cash	875	(1,515)	1,095
Net increase (decrease) in cash, cash equivalents and restricted cash and cash equivalents	35,063	(158,725)	15,162
Cash, cash equivalents and restricted cash and cash equivalents at beginning of year	28,414	187,139	171,977
Cash, cash equivalents and restricted cash and cash equivalents at end of year	63,477	28,414	187,139
Supplemental disclosure of cash flow information:
Common stock and warrants issued for acquisition of other companies	(325)	252,544	0
Addition of finance lease obligations	6,506	7,008	6,439
Recognition of operating lease liabilities and right-of-use assets	22,365	0	0
Common stock contributed to pension plans	3,600	7,595	0
Common stock issued for 401(k) match	3,862	3,705	3,549
Payment of accrued compensation in restricted stock units	8,274	4,863	4,240
Common stock issued for prepayment of debt	33,457	0	0
Marketable equity securities received for sale of mineral interest	2,257	0	0
Cash received (paid) during year for:
Interest, net of amount capitalized	(42,972)	(38,400)	(35,624)
Income tax (payments) receipts	$ (3,385)	$ 115	$ (23,128)