Commitments and Contingencies - Changes in Accrued Environmental Remediation and Related Costs (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Balance at the beginning of the period	$ 116,658
Additions charged to expense, net	3,147
Payments, net	(646)
Balance at the end of the period	119,159
Amounts recognized in the Condensed Consolidated Balance Sheet at the end of the period:
Current liability		$ 13,101	$ 13,350
Noncurrent liability		106,058	103,308
Balance at the end of the period	$ 116,658	$ 119,159	$ 116,658