Supplementary Information on Oil and Gas Operations—Unaudited - Changes in Standardized Measure (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Roll Forward]
Standardized measure at beginning of year	$ 548,562	$ 451,180	$ 230,823
Sales and transfers of oil and gas produced, net of production costs	(55,849)	(173,540)	(134,184)
Changes in price, net of future production costs	(267,710)	37,204	55,601
Extensions and discoveries, net of future production and development costs	70,928	237,290	70,181
Changes in estimated future development costs, net of development costs incurred during this period	31,007	11,094	(25,389)
Revisions of quantity estimates	(14,427)	25,591	58,508
Accretion of discount	60,071	47,130	23,776
Net change in income taxes	52,149	(32,034)	(13,182)
Purchase of reserves in place	0	0	191,964
Sale of reserves in place	(194,454)	(7,240)	(411)
Changes in production rates (timing) and other	(102,592)	(48,113)	(6,507)
Net increase (decrease) in standardized measure	(420,877)	97,382	220,357
Standardized measure at end of year	$ 127,685	$ 548,562	$ 451,180