Environmental Matters - Environmental Sites (Details) $ in Thousands	1 Months Ended			3 Months Ended
	Jul. 31, 2017 USD ($)	Jan. 31, 2017 USD ($)	May 31, 2012 USD ($)	Mar. 31, 2019 USD ($) property party	Dec. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)
Site Contingency [Line Items]
Current Liabilities				$ 30,143	$ 33,112	$ 16,763
Non-Current Liabilities				94,364	95,636	106,611
Gasco/Siltronic Sediments
Site Contingency [Line Items]
Current Liabilities				4,595	5,117	2,797
Non-Current Liabilities				44,427	44,351	45,015
Site Contingency, Environmental Remediation Costs Recognized				49,000
Gasco/Siltronic Sediments | Minimum [Member]
Site Contingency [Line Items]
Environmental Exit Costs, Anticipated Cost			$ 49,000
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				2,299	2,600	1,769
Non-Current Liabilities				5,958	6,273	3,928
Gasco/Siltronic Upland [Member]
Site Contingency [Line Items]
Current Liabilities				11,951	13,983	11,408
Non-Current Liabilities				43,800	44,830	46,769
Central Service Center [Member]
Site Contingency [Line Items]
Current Liabilities				10	10	25
Non-Current Liabilities				0	0	0
Front Street [Member]
Site Contingency [Line Items]
Current Liabilities				11,288	11,402	764
Non-Current Liabilities				0	3	10,720
Undiscounted environmental remediation expense	$ 10,500
Additional studies and design costs	$ 800
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