Commitments and Contingencies - Changes in Accrued Environmental Remediation and Related Costs (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Balance at the beginning of the period	$ 116,658
Additions charged to expense, net	3,236
Payments, net	(4,628)
Balance at the end of the period	115,266
Amounts recognized in the Condensed Consolidated Balance Sheet at the end of the period:
Current liability		$ 11,400	$ 13,350
Noncurrent liability		103,866	103,308
Balance at the end of the period	$ 116,658	$ 115,266	$ 116,658