Environmental Matters - Environmental Sites (Details) $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended
	Jan. 31, 2017 USD ($)	Jun. 30, 2020 USD ($) party property	Jun. 30, 2020 USD ($) party property	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)
Site Contingency [Line Items]
Current Liabilities		$ 34,066	$ 34,066	$ 39,225	$ 17,578
Non-Current Liabilities		91,289	91,289	96,797	103,020
Gasco/Siltronic Sediments
Site Contingency [Line Items]
Current Liabilities		10,431	10,431	11,632	4,403
Non-Current Liabilities		41,945	41,945	46,082	44,374
Site Contingency, Environmental Remediation Costs Recognized		52,400	52,400
Gasco/Siltronic Sediments | Minimum [Member]
Site Contingency [Line Items]
Environmental Exit Costs, Anticipated Cost			52,400
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		2,434	2,434	2,543	2,150
Non-Current Liabilities		$ 6,228	$ 6,228	6,920	5,645
Gasco Uplands [Member]
Site Contingency [Line Items]
Site contingency: number of management pieces		2	2
Gasco/Siltronic Upland [Member]
Site Contingency [Line Items]
Current Liabilities		$ 10,979	$ 10,979	14,203	9,964
Non-Current Liabilities		41,878	41,878	43,616	42,672
Central Service Center [Member]
Site Contingency [Line Items]
Current Liabilities		0	0	0	10
Non-Current Liabilities		0	$ 0	0	0
Environmental monitoring activities, duration			5 years
Front Street [Member]
Site Contingency [Line Items]
Current Liabilities		10,222	$ 10,222	10,847	1,051
Non-Current Liabilities		1,059	1,059	0	10,150
Undiscounted environmental remediation expense		8,800
Additional studies and design costs			2,500
Oregon Steel Mills [Member]
Site Contingency [Line Items]
Current Liabilities		0	0	0	0
Non-Current Liabilities		$ 179	$ 179	$ 179	$ 179
Portland Harbor [Member]
Site Contingency [Line Items]
Number of potentially responsible parties (more than) | party		100	100
EPA final feasibility study and proposed remediation plan, clean-up costs, portland harbor	$ 1,050,000
Number of remediation projects | property		2	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	29
NRD liability claim yakama nation		$ 300	$ 300
Number of Amended Complaints Filed			2