Environmental Matters - Environmental Sites (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Site Contingency [Line Items]
Current Liabilities	$ 10,653	$ 14,475	$ 12,331
Non-Current Liabilities	107,139	105,268	105,167
Gasco/Siltronic Sediments
Site Contingency [Line Items]
Current Liabilities	860	869	1,726
Non-Current Liabilities	43,796	43,972	42,880
Other Portland Harbor
Site Contingency [Line Items]
Current Liabilities	1,379	1,970	1,461
Non-Current Liabilities	3,618	4,148	4,362
Gasco/Siltronic Upland site
Site Contingency [Line Items]
Current Liabilities	7,537	10,657	8,191
Non-Current Liabilities	48,758	49,183	49,928
Central Service Center site
Site Contingency [Line Items]
Current Liabilities	31	73	112
Non-Current Liabilities	0	0	0
Front Street site
Site Contingency [Line Items]
Current Liabilities	846	906	841
Non-Current Liabilities	10,788	7,786	7,818
Oregon Steel Mills
Site Contingency [Line Items]
Current Liabilities	0	0	0
Non-Current Liabilities	$ 179	$ 179	$ 179