Contingencies Remediation Liability (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Accrued Environmental Loss Contingencies, Current	$ 13,831	$ 17,067	$ 18,176
Accrual for Environmental Loss Contingencies, Charges to Expense for New Losses	1,145	307
Accrual for Environmental Loss Contingencies Payments, Net of Reimbursements	$ (4,381)	$ (1,416)