Investment in Unconsolidated Affiliate - Summarized Financial Information for the Gulf LNG Holdings (Detail) - Gulf LNG Holdings Group, LLC Acquisition [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Balance sheets
Current assets	$ 7,737		$ 7,737		$ 7,474
Noncurrent assets	831,662		831,662		855,703
Total assets	839,399		839,399		863,177
Current liabilities	79,893		79,893		83,825
Long-term liabilities	579,506		579,506		621,802
Member’s equity	180,000		180,000		157,550
Total liabilities and member’s equity	839,399		839,399		$ 863,177
Income statements
Revenues	46,548	$ 46,484	139,593	$ 139,452
Total operating costs and expenses	13,965	14,275	42,901	42,233
Operating income	32,583	32,209	96,692	97,219
Net income	$ 23,556	$ 24,340	$ 70,182	$ 72,076