Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Revenue	$ 195,040	$ 199,469	$ 162,123	$ 154,870	$ 143,855	$ 148,795	$ 169,987	$ 163,267	$ 711,502		$ 625,904		$ 709,598
COSTS AND EXPENSES
Amortization	48,118	45,678	43,204	41,876	37,053	31,184	29,459	30,777	178,876		128,473		146,549
General and administrative									34,493		31,345		33,616
Impairment of Long-Lived Assets Held-for-use									250,814		0		0
Pre-development, reclamation, and other									18,421		20,043		18,936
Total costs and expenses									1,056,312		646,208		669,672
OTHER INCOME (EXPENSE), NET
Loss on debt extinguishments									(1,281)		0		(9,342)
Fair value adjustments, net, pretax									16,030		3,638		(864)
Interest expense, net of capitalized interest									(24,771)		(24,364)		(16,440)
Other, net									(3,193)		(24,705)		26,643
Total other income (expense), net									(13,215)		(45,431)		(3)
Total									(358,025)		(65,735)		39,923
Income and mining tax (expense) benefit									11,129		16,780		(28,998)
Income (loss) from continuing operations	(270,961)	(14,277)	(36,764)	(24,894)	468	(53,044)	2,930	691	(346,896)		(48,955)		10,925
Income (loss) from discontinued operations	0	0	0	5,693	0	0	0	550	5,693		550		(12,244)
NET INCOME (LOSS)	$ (270,961)	$ (14,277)	$ (36,764)	$ (19,201)	$ 468	$ (53,044)	$ 2,930	$ 1,241	(341,203)		(48,405)		(1,319)
OTHER COMPREHENSIVE INCOME (LOSS), Net of Tax:
Unrealized gain (loss) on hedger, net of tax									(136)		0		0
Unrealized gain (loss) on debt and equity securities									59		26		3,227
Reclassification adjustments for impairment of equity securities									0		0		426
Reclassification adjustments for realized (gain) loss on sale of equity securities									0		0		1,354
Other comprehensive income (loss)									(77)		26		5,007
COMPREHENSIVE INCOME (LOSS)									$ (341,280)		$ (48,379)		$ 3,688
Basic EPS
Income (Loss) from Continuing Operations, Per Basic Share	$ (1.13)	$ (0.06)	$ (0.18)	$ (0.12)	$ 0	$ (0.29)	$ 0.02	$ 0	$ (1.59)		$ (0.26)		$ 0.06
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	0.00	0.00	0.00	0.03	0	0	0	0	0.03		0		(0.07)
Earnings Per Share, Basic	(1.13)	(0.06)	(0.18)	(0.09)	0	(0.29)	0.02	0	(1.56)	[1]	(0.26)	[1]	(0.01)	[1]
Diluted EPS
Income (Loss) from Continuing Operations, Per Diluted Share	(1.13)	(0.06)	(0.18)	(0.12)	0	(0.29)	0.02	0	(1.59)		(0.26)		0.06
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	0.00	0.00	0.00	0.03	0	0	0	0	0.03		0		(0.07)
Earnings Per Share, Diluted	$ (1.13)	$ (0.06)	$ (0.18)	$ (0.09)	$ 0	$ (0.29)	$ 0.02	$ 0	$ (1.56)	[1]	$ (0.26)	[1]	$ (0.01)	[1]
Product
COSTS AND EXPENSES
Costs applicable to sales	$ 146,631	$ 140,952	$ 131,948	$ 131,650	$ 116,507	$ 116,857	$ 108,246	$ 99,340	$ 551,181	[2]	$ 440,950	[2]	$ 440,260	[2]
Mineral, Exploration
COSTS AND EXPENSES
Costs applicable to sales	$ 7,201	$ 5,893	$ 5,719	$ 3,714	$ 4,128	$ 8,157	$ 6,429	$ 6,683	22,527		$ 25,397		$ 30,311
Impairment of Long-Lived Assets Held-for-use									$ 250,814

[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.