Environmental Matters - Environmental Sites (Details) $ in Thousands	1 Months Ended			6 Months Ended
	Jul. 31, 2017 USD ($)	Jan. 31, 2017 USD ($)	May 31, 2012 USD ($)	Jun. 30, 2018 USD ($) property party	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)
Site Contingency [Line Items]
Current Liabilities				$ 14,496	$ 19,088	$ 13,221
Non-Current Liabilities				105,641	108,280	107,568
Gasco/Siltronic Sediments
Site Contingency [Line Items]
Current Liabilities				2,174	2,683	1,485
Non-Current Liabilities				45,330	45,346	43,376
Site Contingency, Environmental Remediation Costs Recognized				47,500
Gasco/Siltronic Sediments | Minimum
Site Contingency [Line Items]
Environmental Exit Costs, Anticipated Cost			$ 47,500
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				1,444	1,949	1,435
Non-Current Liabilities				3,871	4,163	3,906
Gasco/Siltronic Upland [Member]
Site Contingency [Line Items]
Current Liabilities				9,947	13,422	9,441
Non-Current Liabilities				45,578	47,835	49,319
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				906	1,009	829
Non-Current Liabilities				10,683	10,757	10,788
Undiscounted environmental remediation expense	$ 10,500
Additional studies and design costs	$ 1,100
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