Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended	12 Months Ended			58 Months Ended
	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
Operating activities:
Net loss		$ (16,790)	$ (99,557)	$ (26,563)
Non-cash elements included in net loss:
Depreciation, depletion and amortization		164,026	204,475	140,905
(Gain) loss on disposition of investments		0	(923)	34
Unrealized (gain) loss on investments		(10,268)	2,389	2,816
Adjustment of inventory to market value		0	1,399	8,191
Fee on prepayment of debt with shares of common stock		0	2,855	0
Loss (gain) on disposition of properties, plants, equipment and mineral interests		572	4,643	(2,793)
Provision for reclamation and closure costs		6,189	6,914	6,090
Deferred income taxes		(5,505)	(33,387)	(9,699)
Stock compensation		6,458	5,668	6,278
Amortization of loan origination fees		3,666	2,637	2,077
Loss (gain) on derivative contracts		5,578	5,613	(15,366)
Foreign exchange loss (gain)		2,680	8,025	(7,104)
Foundation grant		1,970	0	0
Other non-cash items		(176)	42	(66)
Change in assets and liabilities, net of business acquired:
Accounts receivable		(1,080)	(10,939)	9,843
Inventories		(13,208)	16,146	(27,512)
Other current and non-current assets		2,381	15,618	(1,726)
Accounts payable and accrued liabilities		19,379	(24,355)	17,795
Accrued payroll and related benefits		14,445	9,226	(2,425)
Accrued taxes		3,561	(3,155)	645
Accrued reclamation and closure costs and other non-current liabilities		(3,085)	7,532	(7,199)
Net cash provided by operating activities		180,793	120,866	94,221
Investing activities:
Additions to properties, plants, equipment and mineral interests		(91,016)	(121,421)	(136,933)
Proceeds from sale of investments		0	1,760	0
Proceeds from disposition of properties, plants and equipment		331	183	2,411
Insurance proceeds received for damaged property		0	0	4,377
Purchases of investments		(2,216)	(389)	(31,971)
Maturities of investments		0	0	64,895
Purchase of other companies, net of cash and restricted cash acquired		0	0	(139,326)
Net cash used in investing activities		92,901	119,867	236,547
Financing activities:
Proceeds from issuance of common stock, net of offering costs	$ 49,000	0	49,019	6,744	$ 73,500
Dividends paid to common stockholders		(8,600)	(4,914)	(4,393)
Dividend paid to preferred stockholders		(552)	(552)	(552)
Debt issuance and credit facility fees paid		(1,356)	(976)	(2,638)
Acquisition of treasury shares from employee equity awards		(2,745)	(2,231)	(2,694)
Borrowings on debt		716,327	279,500	102,024
Repayments of debt		(716,500)	(279,500)	(106,036)
Repayments of finance leases		(5,953)	(7,157)	(7,339)
Net cash (used in) provided by financing activities		(19,379)	33,189	(14,884)
Effect of exchange rates on cash		(1,107)	875	(1,515)
Net increase (decrease) in cash, cash equivalents and restricted cash and cash equivalents		67,406	35,063	(158,725)
Cash, cash equivalents and restricted cash and cash equivalents at beginning of year		63,477	28,414	187,139
Cash, cash equivalents and restricted cash and cash equivalents at end of year	$ 63,477	130,883	63,477	28,414	$ 130,883
Supplemental disclosure of cash flow information:
Interest		(34,853)	(42,972)	(38,400)
Income taxes		7,913	(3,385)	115
Significant non-cash investing and financing activities:
Common stock and warrants issued for acquisition of other companies		0	(325)	252,544
Addition of finance lease obligations		9,113	6,506	7,008
Recognition of operating lease liabilities and right-of-use assets		0	22,365	0
Common stock contributed to pension plans		16,032	3,600	7,595
Common stock issued for 401(k) match		4,624	3,862	3,705
Payment of accrued compensation in restricted stock units		5,096	8,274	4,863
Common stock issued for prepayment of debt		0	33,457	0
Marketable equity securities received for sale of mineral interest		$ 0	$ 2,257	$ 0