Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Revenue		$ 169,987	$ 149,540	$ 333,254	$ 335,094
COSTS AND EXPENSES
Costs applicable to sales	[1]	108,246	102,229	207,586	216,719
Amortization		29,459	30,734	60,236	69,427
General and administrative		7,650	7,025	16,454	17,150
Exploration		6,429	7,813	13,112	13,065
Pre-development, reclamation, and other		3,620	4,085	7,845	7,922
Total costs and expenses		155,404	151,886	305,233	324,283
OTHER INCOME (EXPENSE), NET
Loss on debt extinguishments		0	(9,342)	0	(9,342)
Fair value adjustments, net, pretax		(2,462)	336	2,192	(864)
Interest expense, net of capitalized interest		(6,018)	(3,744)	(11,983)	(7,323)
Other, net		544	3,974	1,057	24,773
Total other income (expense), net		(7,936)	(8,776)	(8,734)	7,244
Total		6,647	(11,122)	19,287	18,055
Income and mining tax (expense) benefit		(3,717)	1,127	(15,666)	(9,751)
Income (loss) from continuing operations		2,930	(9,995)	3,621	8,304
Income (loss) from discontinued operations		0	(960)	550	(596)
NET INCOME (LOSS)		2,930	(10,955)	4,171	7,708
OTHER COMPREHENSIVE INCOME (LOSS), Net of Tax:
Unrealized gain (loss) on debt and equity securities		(87)	(18)	(365)	(2,200)
Reclassification adjustments for impairment of equity securities		0	305		426
Reclassification adjustments for realized (gain) loss on sale of equity securities		0	(203)		1,268
Other comprehensive income (loss)		(87)	84	(365)	(506)
COMPREHENSIVE INCOME (LOSS)		$ 2,843	$ (10,871)	$ 3,806	$ 7,202
Basic EPS
Income (Loss) from Continuing Operations, Per Basic Share		$ 0.016	$ (0.056)	$ 0.020	$ 0.046
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share		0.000	(0.005)	0.003	(0.003)
Earnings Per Share, Basic		0.016	(0.061)	0.023	0.043
Diluted EPS
Income (Loss) from Continuing Operations, Per Diluted Share		0.016	(0.056)	0.019	0.045
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share		0.000	(0.005)	0.003	(0.003)
Earnings Per Share, Diluted		$ 0.016	$ (0.061)	$ 0.022	$ 0.042

[1] Excludes amortization.