Commitments and Contingencies - Changes in Accrued Environmental Remediation and Related Costs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments And Contingencies Disclosure [Abstract]
Balance at the beginning of the year	$ 116,658	$ 113,133	$ 110,015
Additions charged to expense, net	3,376	5,152	4,370
Payments, net	(8,125)	(1,627)	(1,252)
Balance at the end of the year	111,909	116,658	113,133
Amounts recognized in the Condensed Consolidated Balance Sheet at the end of the period:
Current liability				$ 5,302	$ 13,350	$ 8,668
Noncurrent liability				106,607	103,308	104,465
Balance at the end of the year	$ 116,658	$ 113,133	$ 110,015	$ 111,909	$ 116,658	$ 113,133