Environmental Matters - Environmental Sites (Details) $ in Thousands	1 Months Ended			9 Months Ended
	Jul. 31, 2017 USD ($)	Jan. 31, 2017 USD ($)	May 31, 2012 USD ($)	Sep. 30, 2018 USD ($) property party	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)
Site Contingency [Line Items]
Current Liabilities				$ 18,746	$ 19,088	$ 10,653
Non-Current Liabilities				97,781	108,280	107,139
Gasco/Siltronic Sediments
Site Contingency [Line Items]
Current Liabilities				2,471	2,683	860
Non-Current Liabilities				44,410	45,346	43,796
Site Contingency, Environmental Remediation Costs Recognized				46,900
Gasco/Siltronic Sediments | Minimum
Site Contingency [Line Items]
Environmental Exit Costs, Anticipated Cost			$ 46,900
Gasco/Siltronic Sediments | Maximum
Site Contingency [Line Items]
Environmental Exit Costs, Anticipated Cost			$ 350,000
Portland Harbor Other [Member]
Site Contingency [Line Items]
Current Liabilities				1,392	1,949	1,379
Non-Current Liabilities				3,540	4,163	3,618
Gasco/Siltronic Upland [Member]
Site Contingency [Line Items]
Current Liabilities				8,847	13,422	7,537
Non-Current Liabilities				44,310	47,835	48,758
Central Service Center [Member]
Site Contingency [Line Items]
Current Liabilities				25	25	31
Non-Current Liabilities				0	0	0
Front Street [Member]
Site Contingency [Line Items]
Current Liabilities				6,011	1,009	846
Non-Current Liabilities				5,342	10,757	10,788
Undiscounted environmental remediation expense	$ 10,500
Additional studies and design costs	$ 900
Oregon Steel Mills [Member]
Site Contingency [Line Items]
Current Liabilities				0	0	0
Non-Current Liabilities				$ 179	$ 179	$ 179
Portland Harbor [Member]
Site Contingency [Line Items]
Number of potentially responsible parties (more than) | party				100
EPA final feasibility study and proposed remediation plan, clean-up costs, portland harbor		$ 1,050,000
Number of remediation projects | property				2
Portland Harbor [Member] | Minimum
Site Contingency [Line Items]
Percentage of clean-up costs		(30.00%)
Portland Harbor [Member] | Maximum
Site Contingency [Line Items]
Percentage of clean-up costs		50.00%
Yakama Nation [Member] | Portland Harbor Other [Member]
Site Contingency [Line Items]
Trustee Council Members - Number of Claimants				1
Site Contingency, Number of Other Third-Party Defendants					29
NRD liability claim yakama nation					$ 300
Number of Amended Complaints Filed				2