Firm Transportation Obligation - Summary of Restructuring Related Obligations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Restructuring Reserve [Roll Forward]
Balance at beginning of period	$ 14,790	$ 15,993	$ 17,082
Accretion of obligations	942	1,301	1,674
Cash payments, net	(2,271)	(2,504)	(2,763)
Balance at end of period	$ 13,461	$ 14,790	$ 15,993