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 ($)	Sep. 30, 2019 USD ($) party property	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)
Site Contingency [Line Items]
Current Liabilities				$ 22,403	$ 33,112	$ 18,746
Non-Current Liabilities				96,662	95,636	97,781
Gasco/Siltronic Sediments
Site Contingency [Line Items]
Current Liabilities				5,976	5,117	2,471
Non-Current Liabilities				43,861	44,351	44,410
Site Contingency, Environmental Remediation Costs Recognized				49,800
Gasco/Siltronic Sediments | Minimum [Member]
Site Contingency [Line Items]
Environmental Exit Costs, Anticipated Cost			$ 49,800
Gasco/Siltronic Sediments | Maximum [Member]
Site Contingency [Line Items]
Environmental Exit Costs, Anticipated Cost			$ 350,000
Portland Harbor Other [Member]
Site Contingency [Line Items]
Current Liabilities				2,211	2,600	1,392
Non-Current Liabilities				5,331	6,273	3,540
Gasco/Siltronic Upland [Member]
Site Contingency [Line Items]
Current Liabilities				8,202	13,983	8,847
Non-Current Liabilities				42,267	44,830	44,310
Central Service Center [Member]
Site Contingency [Line Items]
Current Liabilities				5	10	25
Non-Current Liabilities				0	0	0
Front Street [Member]
Site Contingency [Line Items]
Current Liabilities				6,009	11,402	6,011
Non-Current Liabilities				5,024	3	5,342
Undiscounted environmental remediation expense	$ 10,500
Additional studies and design costs				500
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 [Member]
Site Contingency [Line Items]
Percentage of clean-up costs		(30.00%)
Portland Harbor [Member] | Maximum [Member]
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