Commitments and Contingencies - Changes in Accrued Environmental Remediation and Related Costs (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commitments And Contingencies Disclosure [Abstract]
Balance at the beginning of the year	$ 113,636	$ 48,006	$ 41,637
Additions charged to expense, net	6,485	68,929	14,467
Payments, net	(10,106)	(3,299)	(8,098)
Balance at the end of the year	110,015	113,636	48,006
Amounts recognized in the Condensed Consolidated Balance Sheet at the end of the period:
Current liability	6,984	4,859	5,667
Noncurrent liability	103,031	108,777	42,339
Balance at the end of the year	$ 110,015	$ 113,636	$ 48,006