Contingencies - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended		6 Months Ended	12 Months Ended
	Apr. 30, 2016	Oct. 31, 2011	Mar. 31, 2017	Jun. 30, 2016	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2005	Dec. 31, 2016
Loss Contingencies [Line Items]
Other current liabilities			$ 12,780					$ 13,083
Other liabilities			7,923					$ 9,235
New Almaden Mine [Member] | Natural Resource Damage Claim [Member]
Loss Contingencies [Line Items]
Expense recognized					$ 1,200		$ 800
Total reserve			1,500
Other current liabilities			200
Other liabilities			1,300
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
Escrow deposit due to be settled date			2016-08
Pending Litigation [Member] | New Idria Mercury Mine [Member] | EPA Notice Letter [Member]
Loss Contingencies [Line Items]
Expense recognized		$ 1,900		$ 1,000
Loss contingency costs			$ 1,600
Accrued balance						$ 1,300
Total reserve			2,400
Other current liabilities			300
Other liabilities			$ 2,100