Supplemental Oil and Gas Reserve Information (Details 1) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Abstract]
Future cash inflows	$ 1,035,786	$ 1,721,207	$ 5,479,211
Future costs, production	(424,092)	(711,887)	(1,719,989)
Future costs, abandonment	(65,852)	(120,737)	(149,112)
Future costs, development	(148,108)	(147,189)	(695,180)
Future costs, income taxes	(12,204)	(38,306)	(833,601)
Future net cash flows	385,530	703,088	2,081,329
10% discount factor	(226,567)	(312,445)	(1,148,416)
Standardized measure of discounted net cash flows	$ 158,963	$ 390,643	$ 932,913	$ 926,923