Contingencies - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended		12 Months Ended				87 Months Ended
	Jan. 31, 2019	Apr. 30, 2016	Dec. 31, 2018	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2005	Dec. 31, 2018
Loss Contingencies [Line Items]
Other current liabilities			$ 16,701		$ 16,701	$ 15,472			$ 16,701
Other liabilities			19,794		19,794	8,236			19,794
Annual rent					3,312	3,198	$ 3,625
New Idria Mercury Mine [Member]
Loss Contingencies [Line Items]
Financial assurance required to be provided to EPA to secure performance			2,000
New Almaden Mine (Formerly Referred to as Guadalupe River Watershed) [Member] | Natural Resource Damage Claim [Member]
Loss Contingencies [Line Items]
Total reserve			1,500		1,500	1,500			1,500
Other current liabilities			300		300				300
Other liabilities			1,200		1,200				1,200
Expense recognized				$ 1,200			1,200	$ 800
Accrued balance					500
Original estimated project costs		$ 1,600
Revised estimated project costs, Low Estimate		3,300
Revised estimated project costs, High Estimate		$ 4,400
Lawn and Garden Indemnification Claim [Member]
Loss Contingencies [Line Items]
Indemnification claims					10,000
Escrow deposit			8,600		$ 8,600				8,600
Escrow deposit due to be settled date					2016-08
Discontinued operations pre-tax charge					$ 1,225
Amount of escrow deposits expected to release upon settlement of agreement					$ 7,400
Lawn and Garden Indemnification Claim [Member] | Guarantee Obligation [Member]
Loss Contingencies [Line Items]
Lease expiring period					September 2025
Annual rent					$ 2,000
Liabilities and related pre tax charges					10,300
Lease liabilities			10,400		10,400				10,400
Subsequent Event [Member] | New Idria Mercury Mine [Member]
Loss Contingencies [Line Items]
Prepayment amount	$ 200
Pending Litigation [Member] | New Idria Mercury Mine [Member] | EPA Notice Letter [Member]
Loss Contingencies [Line Items]
Loss contingencies, payments									2,500
Loss contingency, Loss in period					200	1,300	$ 1,000		5,900
Total reserve			3,400		3,400	$ 3,600			3,400
Other current liabilities			900		900				900
Other liabilities			$ 2,500		$ 2,500				$ 2,500