Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Site Contingency [Line Items]
Environmental and legal losses	$ 24,200,000	$ 25,800,000
Cash outlays related to legal and environmental matters	$ 2,000,000	$ 1,400,000
Contribution for future response costs	5.00%
Wilmington Site [Member]
Site Contingency [Line Items]
Payment of environmental response costs	$ 2,500,000
Minimum [Member]
Site Contingency [Line Items]
Environmental and legal losses	24,200,000
Maximum [Member]
Site Contingency [Line Items]
Environmental and legal losses	$ 45,400,000