Environmental Matters - Environmental Sites (Details) $ in Thousands	1 Months Ended	3 Months Ended
	May 31, 2012 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)	Jan. 31, 2017 USD ($)
Site Contingency [Line Items]
Current Liabilities		$ 16,763	$ 19,088	$ 14,638
Non-Current Liabilities		106,611	108,280	105,285
Gasco/Siltronic Sediments
Site Contingency [Line Items]
Current Liabilities		2,797	2,683	1,573
Non-Current Liabilities		45,015	45,346	43,200
Other Portland Harbor
Site Contingency [Line Items]
Current Liabilities		1,769	1,949	1,804
Non-Current Liabilities		3,928	4,163	3,940
Gasco/Siltronic Upland site
Site Contingency [Line Items]
Current Liabilities		11,408	13,422	10,335
Non-Current Liabilities		46,769	47,835	50,189
Central Service Center site
Site Contingency [Line Items]
Current Liabilities		25	25	68
Non-Current Liabilities		0	0	0
Front Street site
Site Contingency [Line Items]
Current Liabilities		764	1,009	858
Non-Current Liabilities		10,720	10,757	7,777
Oregon Steel Mills
Site Contingency [Line Items]
Current Liabilities		0	0	0
Non-Current Liabilities		179	179	179
Gasco/Siltronic Sediments
Site Contingency [Line Items]
Site Contingency, Environmental Remediation Costs Recognized		$ 47,800
Gasco/Siltronic Sediments | Minimum [Member]
Site Contingency [Line Items]
Environmental Exit Costs, Anticipated Cost	$ 47,800
Gasco/Siltronic Sediments | Maximum [Member]
Site Contingency [Line Items]
Environmental Exit Costs, Anticipated Cost	$ 350,000
Yakama Nation [Member] | Portland Harbor [Member]
Site Contingency [Line Items]
Number of Amended Complaints Filed		2
Trustee Council Members - Number of Claimants		1
Site Contingency, Number of Other Third-Party Defendants		29
NRD liability claim yakama nation					$ 300
Environmental Restoration Costs [Member] | Front Street site
Site Contingency [Line Items]
Remediation Non-recovery Amount		$ 400	$ 400	$ 400