Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities:
Net income (loss)	$ 69,547	$ (86,968)	$ 17,824
Non-cash elements included in net income (loss):
Depreciation, depletion and amortization	117,413	112,585	112,173
Net loss on sale of investments		44
Unrealized loss on investments	177	3,333	3,224
Adjustment of inventory to market value	811	1,649
(Gain) loss on disposition of properties, plants, equipment and mineral interests	(147)	404	(25)
Provision for reclamation and closure costs	4,813	12,036	10,215
Deferred income taxes	2,112	54,978	1,895
Stock compensation	6,184	5,425	4,965
Acquisition costs	1,048
Amortization of loan origination fees	1,871	1,821	2,183
(Gain) loss on derivative contracts	(5,494)	11,630	(6,886)
Foreign exchange loss (gain)	4,649	(20,081)	(10,482)
Other non-cash items	(174)	(35)	(858)
Change in assets and liabilities, net of business acquired:
Accounts receivable	4,233	(6,834)	3,091
Inventories	(5,697)	(854)	1,119
Other current and non-current assets	14,422	1,195	(580)
Accounts payable and accrued liabilities	(6,539)	(4,211)	(19,697)
Accrued payroll and related benefits	17,705	7,325	16,422
Accrued taxes	263	4,653	(3,612)
Accrued reclamation and closure costs and other non-current liabilities	(1,869)	8,350	(47,847)
Net cash provided by operating activities	225,328	106,445	83,124
Investing activities:
Additions to properties, plants, equipment and mineral interests	(164,788)	(137,443)	(122,537)
Proceeds from sale of investments		14
Proceeds from disposition of properties, plants and equipment	348	579	428
Redemptions of restricted cash and investment balances			4,334
Purchases of investments	(48,943)	(947)	(580)
Maturities of investments	18,649
Purchase of other companies, net of cash acquired	(3,931)	(809)
Net cash used by investing activities	(198,665)	(138,606)	(118,355)
Financing activities:
Proceeds from issuance of common stock, net of offering costs	8,121
Proceeds from exercise of warrants			54,418
Dividends paid to common stockholders	(3,867)	(3,739)	(3,547)
Dividend paid to preferred stockholders	(552)	(552)	(552)
Debt issuance and credit facility fees paid	(127)	(127)	(938)
Acquisition of treasury shares	(4,440)	(1,874)	(3,740)
Payments on debt	(2,721)	(870)
Payments on capital leases	(8,435)	(9,981)	(9,137)
Net cash (used in) provided by financing activities	(12,021)	(17,143)	36,504
Effect of exchange rates on cash	(74)	(5,152)	(3,783)
Net increase (decrease) in cash and cash equivalents	14,568	(54,456)	(2,510)
Cash and cash equivalents at beginning of year	155,209	209,665	212,175
Cash and cash equivalents at end of year	169,777	155,209	209,665
Cash received (paid) during year for:
Interest, net of amount capitalized	(19,280)	(22,628)	(23,749)
Income tax (payments) receipts	(6,333)	4,186	7,124
Significant non-cash investing and financing activities:
Common stock issued for acquisition of other companies	48,109	19,133
Capital leases acquired	2,297	5,090	9,475
Payment of accrued compensation in restricted stock units	5,511	3,016	4,600
Senior notes contributed to pension plan, par value			$ 6,500