Condensed Consolidated Statements of Operations and Comprehensive (Loss) Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Sales of products	$ 152,617	$ 139,709
Cost of sales and other direct production costs	110,386	72,869
Depreciation, depletion and amortization	38,787	28,054
Total cost of sales	149,173	100,923
Gross profit	3,444	38,786
Other operating expenses:
General and administrative	9,959	7,735
Exploration	4,402	7,360
Pre-development	856	1,005
Research and development	403	1,436
Other operating expense	587	515
Suspension-related costs	2,778	5,017
Acquisition costs	13	2,507
Provision for closed operations and environmental matters	570	1,262
Total other operating expense	19,568	26,837
(Loss) income from operations	(16,124)	11,949
Other income (expense):
Unrealized gain on investments	96	310
(Loss) gain on derivative contracts	(1,799)	4,007
Net foreign exchange (loss) gain	(3,133)	2,592
Other expense	(1,124)	(56)
Interest expense	(10,665)	(9,794)
Total other expense	(16,625)	(2,941)
(Loss) income before income taxes	(32,749)	9,008
Income tax benefit (provision)	7,216	(768)
Net income (loss)	(25,533)	8,240
Preferred stock dividends	(138)	(138)
(Loss) income applicable to common stockholders	(25,671)	8,102
Comprehensive (loss) income:
Net (loss) income	(25,533)	8,240
Unrealized holding losses on investments		(31)
Change in fair value of derivative contracts designated as hedge transactions	4,259	(2,073)
Comprehensive (loss) income	$ (21,274)	$ 6,136
Basic (loss) income per common share after preferred dividends (in dollars per share)	$ (0.05)	$ 0.02
Diluted (loss) income per common share after preferred dividends (in dollars per share)	$ (0.05)	$ 0.02
Weighted average number of common shares outstanding - basic (in shares)	482,829	399,322
Weighted average number of common shares outstanding - diluted (in shares)	482,829	401,923