Summary of Restructuring Related Obligations (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2009
Restructuring Reserve [Roll Forward]
Balance at beginning of period	$ 17,263	$ 576		$ 64
Employee, office and other costs accrued, net	7	1,284	2,351
Firm transportation charge	0	17,332	0
Accretion of obligations	1,674	570	0
Cash payments, net	(2,854)	(2,499)	(1,839)
Balance at end of period	$ 16,090	$ 17,263	$ 576	$ 64