Supplementary Information on Oil and Gas Operations—Unaudited - Standardized Measure (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Future Net Cash Flows [Abstract]
Future cash flows	$ 487,834	$ 1,711,404	$ 1,243,627
Future production costs	(171,678)	(372,690)	(295,666)
Future development costs	(116,591)	(244,784)	(185,188)
Future income taxes	0	(121,192)	(37,404)
Future net cash flows	199,565	972,738	725,369
10% annual discount	(71,880)	(424,176)	(274,189)
Standardized measure of discounted future net cash flows	$ 127,685	$ 548,562	$ 451,180	$ 230,823