Contingencies - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended				9 Months Ended	12 Months Ended
	Apr. 30, 2016	Oct. 31, 2011	Sep. 30, 2016	Jun. 30, 2016	Jun. 30, 2015	Sep. 30, 2014	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2005
New Almaden Mine (Formerly Referred to as Guadelupe River Watershed) | Natural Resource Damage Claim
Loss Contingencies [Line Items]
Expense recognized			$ 0.6				$ 1.2		$ 0.8
Total reserve			1.6				1.6
Accrued balance							0.3
Original estimated project costs	$ 1.6
Revised estimated project costs, Low Estimate	3.3
Revised estimated project costs, High Estimate	$ 4.4
Lawn and Garden Indemnification Claim
Loss Contingencies [Line Items]
Indemnification claims							10.0
Escrow deposit			8.6				$ 8.6
Escrow deposit due to be settled date							2016-08
Pending Litigation | New Idria Mercury Mine | E P A Notice Letter
Loss Contingencies [Line Items]
Expense recognized		$ 1.9		$ 1.0
Loss contingency costs			1.6				$ 1.6
Accrued balance								$ 1.3
Total reserve			2.6				2.6
Settled Litigation | Patent Infringement Against Orbis Corp | Loss From Patent Infringement
Loss Contingencies [Line Items]
Accrued balance						$ 3.0
Litigation settlement, amount			$ 0.2
Contingency accrual reversal					$ 3.0
Settled Litigation | Patent Infringement Against Orbis Corp | Loss From Patent Infringement | Maximum
Loss Contingencies [Line Items]
Litigation settlement, amount							$ 3.1