Environmental Matters - Environmental Sites $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2017 USD ($)	Mar. 31, 2021 USD ($) party property	Dec. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)
Site Contingency [Line Items]
Current Liabilities		$ 23,594	$ 28,241	$ 37,909
Non-Current Liabilities		89,941	92,281	92,423
Gasco/Siltronic Sediments
Site Contingency [Line Items]
Current Liabilities		7,026	7,596	11,829
Non-Current Liabilities		42,374	43,725	42,837
Site Contingency, Environmental Remediation Costs Recognized		49,400
Gasco/Siltronic Sediments | Minimum [Member]
Site Contingency [Line Items]
Environmental Exit Costs, Anticipated Cost		49,400
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		2,175	1,942	2,554
Non-Current Liabilities		$ 6,954	7,020	6,574
Gasco Uplands [Member]
Site Contingency [Line Items]
Site contingency: number of management pieces		2
Gasco/Siltronic Upland [Member]
Site Contingency [Line Items]
Current Liabilities		$ 13,135	14,887	12,822
Non-Current Liabilities		39,302	40,250	42,833
Front Street [Member]
Site Contingency [Line Items]
Current Liabilities		1,258	3,816	10,704
Non-Current Liabilities		1,132	1,107	0
Additional studies and design costs		2,400
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