Investment in Unconsolidated Affiliate - Summarized Financial Information for the Gulf LNG Holdings (Detail) - Gulf LNG Holdings Group, LLC Acquisition [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Balance sheets
Current assets	$ 7,474	$ 7,523
Noncurrent assets	855,703	889,655
Total assets	863,177	897,178
Current liabilities	83,825	79,970
Long-term liabilities	621,802	678,926
Member’s equity	157,550	138,282
Total liabilities and member’s equity	863,177	897,178
Income statements
Revenues	185,937	186,498
Total operating costs and expenses	56,827	56,379
Operating income	129,110	130,119
Net income	$ 95,455	$ 97,241