Summary of Restructuring Related Obligations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Restructuring Reserve [Roll Forward]
Balance at beginning of period	$ 15,559	$ 16,677	$ 16,090	$ 17,263
Employee, office and other costs accrued, net	18	2	27	5
Accretion of firm transportation obligation	(407)	410	991	1,263
Cash payments, net	(857)	(705)	(1,981)	(2,147)
Balance at end of period	$ 15,127	$ 16,384	$ 15,127	$ 16,384