Consolidated Statements of Comprehensive Income (Loss) - USD ($)		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Revenue		$ 785,461,000		$ 711,502,000		$ 625,904,000
COSTS AND EXPENSES
Amortization		131,387,000		178,876,000		128,473,000
General and administrative		33,722,000		34,493,000		31,345,000
Impairment of Long-Lived Assets Held-for-use		0		250,814,000		0
Pre-development, reclamation, and other		55,654,000		18,421,000		20,043,000
Total costs and expenses		703,741,000		1,056,312,000		646,208,000
OTHER INCOME (EXPENSE), NET
Loss on debt extinguishments		0		(1,281,000)		0
Fair value adjustments, net, pretax		7,601,000		16,030,000		3,638,000
Interest expense, net of capitalized interest		(20,708,000)		(24,771,000)		(24,364,000)
Other, net		(5,941,000)		(3,193,000)		(24,705,000)
Total other income (expense), net		(19,048,000)		(13,215,000)		(45,431,000)
Total		62,672,000		(358,025,000)		(65,735,000)
Income and mining tax (expense) benefit		(37,045,000)		11,129,000		16,780,000
Income (loss) from continuing operations		25,627,000		(346,896,000)		(48,955,000)
Income (loss) from discontinued operations		0		5,693,000		550,000
NET INCOME (LOSS)		25,627,000		(341,203,000)		(48,405,000)
Other comprehensive income (loss), derivatives qualifying as hedges, tax, portion attributable to parent		0		365,000		0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax		1,434,000		0		0
OTHER COMPREHENSIVE INCOME (LOSS), Net of Tax:
Unrealized gain (loss) on hedger, net of tax		(12,434,000)		(136,000)		0
Unrealized gain (loss) on debt and equity securities		0		59,000		26,000
Reclassification adjustments for impairment of equity securities		1,434,000
Other comprehensive income (loss)		(11,000,000)		(77,000)		26,000
COMPREHENSIVE INCOME (LOSS)		$ 14,627,000		$ (341,280,000)		$ (48,379,000)
Basic EPS
Income (Loss) from Continuing Operations, Per Basic Share		$ 0.11		$ (1.59)		$ (0.26)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share		0		0.03		0
Earnings Per Share, Basic		0.11	[1]	(1.56)	[1]	(0.26)
Diluted EPS
Income (Loss) from Continuing Operations, Per Diluted Share		0.11		(1.59)		(0.26)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share		0		0.03		0
Earnings Per Share, Diluted		$ 0.11	[1]	$ (1.56)	[1]	$ (0.26)
Accumulated Deficit [Member]
OTHER INCOME (EXPENSE), NET
NET INCOME (LOSS)		$ 25,627,000		$ (341,203,000)		$ (48,405,000)
Product
COSTS AND EXPENSES
Costs applicable to sales	[2]	440,335,000		551,181,000		440,950,000
Mineral, Exploration
COSTS AND EXPENSES
Costs applicable to sales		42,643,000		22,527,000		25,397,000
Impairment of Long-Lived Assets Held-for-use		$ 0		$ 250,814,000		$ 0

[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.