Commitments and Contingencies - Additional Information (Detail)			12 Months Ended	192 Months Ended
	Jun. 30, 2017 USD ($)	Jan. 06, 2017 USD ($) Segment	Aug. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	May 31, 2017	Apr. 30, 2017	Nov. 30, 2016 USD ($)	Aug. 31, 2015
Commitments and Contingencies Disclosure [Line Items]
Remedial investigation and feasibility study				$ 110,000,000
Equity method investment, percentage of ownership interest			50.00%
Payment to acquire equity method investments			$ 600,000
Note receivable			36,500,000
Performance Guarantee
Commitments and Contingencies Disclosure [Line Items]
Letter of credit facility outstanding amount			$ 77,600,000
Portland Harbor Site
Commitments and Contingencies Disclosure [Line Items]
Number of sediment decision units | Segment		13
Estimated undiscounted cost		$ 1,700,000,000
Period for remedial action		13 years
Period for monitoring		30 years
New data collection period to reflect actual cost prior to final remedy design		2 years
Portland Harbor Site | Minimum
Commitments and Contingencies Disclosure [Line Items]
Accuracy of cost estimate		(30.00%)
Portland Harbor Site | Maximum
Commitments and Contingencies Disclosure [Line Items]
Accuracy of cost estimate		50.00%
GBW Railcar Services LLC
Commitments and Contingencies Disclosure [Line Items]
Equity method investment, percentage of ownership interest			50.00%					50.00%
Note receivable			$ 36,500,000
Amsted-Maxion Cruzeiro
Commitments and Contingencies Disclosure [Line Items]
Equity method investment, percentage of ownership interest			24.50%		24.50%	19.50%
Note receivable			$ 10,000,000
Pending Litigation | Commercial Litigation in a Foreign Jurisdictions
Commitments and Contingencies Disclosure [Line Items]
Adverse judgment							$ 15,000,000
Adverse judgment	$ 10,000,000