Commitments and Contingencies - Changes in Accrued Environmental Remediation and Related Costs (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015	Dec. 31, 2014
Commitments And Contingencies Disclosure [Abstract]
Balance at the beginning of the period	$ 110,015
Additions charged to expense, net	2,530
Payments, net	(934)
Balance at the end of the period	111,611
Amounts recognized in the Condensed Consolidated Balance Sheet at the end of the period:
Current liability		$ 6,989	$ 6,984
Noncurrent liability		104,622	103,031
Balance at the end of the period	$ 110,015	$ 111,611	$ 110,015