Commitments and Contingencies - Changes in Accrued Environmental Remediation and Related Costs (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Commitments And Contingencies Disclosure [Abstract]
Balance at the beginning of the period	$ 113,636
Additions charged to expense, net	6,055
Payments, net	(2,721)
Balance at the end of the period	116,970
Amounts recognized in the Condensed Consolidated Balance Sheet at the end of the period:
Current liability	12,681	4,859
Noncurrent liability	104,289	108,777
Balance at the end of the period	$ 116,970