Supplemental Oil and Gas Reserve Information (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Roll Forward]
Standardized measure, beginning of period	$ 390,643	$ 932,913	$ 926,923
Net changes in sales prices, net of production costs	(71,603)	(965,126)	(94,104)
Revisions of quantity estimates	329	(245,035)	(234,612)
Accretion of discount	44,278	137,998	138,095
Changes in future development costs, including development costs incurred that reduced future development costs	10,145	308,261	146,392
Changes in timing and other	(29,458)	(69,160)	(70,774)
Net change in income taxes	9,068	395,888	2,893
Future abandonment cost, net of salvage	(2,357)	(2,968)	4,066
Extensions and discoveries	39,678	48,367	431,895
Sales, net of production costs	84,384	126,455	309,758
Sales of minerals-in-place	(147,376)	(24,040)	(8,103)
Standardized measure, end of period	$ 158,963	$ 390,643	$ 932,913