Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue		$ 162,123		$ 169,987		$ 316,993	$ 333,254
COSTS AND EXPENSES
Amortization		43,204		29,459		85,080	60,236
General and administrative		7,750		7,650		17,224	16,454
Pre-development, reclamation, and other		4,334		3,620		8,768	7,845
Total costs and expenses		192,955		155,404		384,103	305,233
OTHER INCOME (EXPENSE), NET
Fair value adjustments, net, pretax		(5,296)		(2,462)		3,824	2,192
Interest expense, net of capitalized interest		(6,825)		(6,018)		(13,279)	(11,983)
Other, net		643		544		703	1,057
Total other income (expense), net		(11,478)		(7,936)		(8,752)	(8,734)
Total		(42,310)		6,647		(75,862)	19,287
Income and mining tax (expense) benefit		5,546		(3,717)		14,204	(15,666)
Income (loss) from continuing operations		(36,764)		2,930		(61,658)	3,621
Income (loss) from discontinued operations		0		0		5,693	550
NET INCOME (LOSS)		(36,764)	$ (19,201)	2,930	$ 1,241	(55,965)	4,171
OTHER COMPREHENSIVE INCOME (LOSS), Net of Tax:
Unrealized gain (loss) on debt and equity securities		0		(87)		59	(365)
Other comprehensive income (loss)		0	$ 59	(87)	$ (278)	59	(365)
COMPREHENSIVE INCOME (LOSS)		$ (36,764)		$ 2,843		$ (55,906)	$ 3,806
Basic EPS
Income (Loss) from Continuing Operations, Per Basic Share		$ (0.18)		$ 0.02		$ (0.30)	$ 0.02
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share		0		0		0.03	0
Earnings Per Share, Basic	[1]	(0.18)		0.02		(0.27)	0.02
Diluted EPS
Income (Loss) from Continuing Operations, Per Diluted Share		(0.18)		0.02		(0.30)	0.02
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share		0		0		0.03	0
Earnings Per Share, Diluted	[1]	$ (0.18)		$ 0.02		$ (0.27)	$ 0.02
Product [Member]
COSTS AND EXPENSES
Costs applicable to sales	[2]	$ 131,948		$ 108,246		$ 263,598	$ 207,586
Mineral, Exploration [Member]
COSTS AND EXPENSES
Costs applicable to sales		$ 5,719		$ 6,429		$ 9,433	$ 13,112

[1] Due to rounding, the sum of net income per share from continuing operations and discontinued operations may not equal net income per share.

[2] Excludes amortization.