Summary of Restructuring Related Obligations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Restructuring Reserve [Roll Forward]
Balance at beginning of period	$ 16,677	$ 251	$ 17,263	$ 576
Employee, office and other costs accrued, net	2	1,431	5	1,283
Loss on long-term purchase commitment	0	17,332	0	17,332
Accretion of firm transportation obligation	410	0	1,263	0
Cash payments, net	(705)	(1,359)	(2,147)	(1,536)
Balance at end of period	$ 16,384	$ 17,655	$ 16,384	$ 17,655