Summary of Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Pre-development, reclamation, and other									18,421		20,043		18,936
Amortization	48,118	45,678	43,204	41,876	37,053	31,184	29,459	30,777	178,876		128,473		146,549
Gross Profit	291	12,839	(13,029)	(18,656)	(9,705)	754	32,282	33,150
Other Cost and Expense, Operating	263,250	14,486	12,084	13,908	11,239	15,850	11,270	13,029
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)
Cash provided by (used in) operating activities	39,295	41,996	26,435	(15,846)	72	5,789	(1,294)	15,541	91,880		17,418		208,456
Capital expenditures	$ (20,907)	$ (30,678)	$ (20,749)	$ (27,438)	$ (17,805)	$ (39,472)	$ (41,165)	$ (42,345)	$ (99,772)		$ (140,787)		$ (136,734)
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]
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 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 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

[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.