Oil and Gas Reserves Information (Unaudited) - Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Reserves (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash Flows Relating to Proved Reserves:
Future Cash Flows	$ 2,267,877	$ 1,763,146
Future Costs:
Production	(798,454)	(705,146)
Development and Abandonment	(502,848)	(362,874)
Future Income Taxes	(6,488)	(1,231)
Future Net Cash Flows	960,087	693,895
10% Discount Factor	(530,812)	(321,756)
Standardized Measure of Discounted Future Net Cash Flows	$ 429,275	$ 372,139	$ 1,090,660	$ 807,217