Supplemental Oil and Natural Gas Disclosure (Unaudited) - Standardized Measure of Discounted Future Net Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Discounted Future Net Cash Flows Relating To Proved Oil And Gas Reserves [Line Items]
Future cash inflows	$ 1,643,582	$ 1,267,179	$ 1,211,290
Future production costs	(211,064)	(193,749)	(205,861)
Future development costs	(70,111)	(36,509)	(84,746)
Future income tax expense	(2,655)	(3,516)	0
Future net cash flows (undiscounted)	1,359,752	1,033,405	920,683
Annual discount 10% for estimated timing	(497,103)	(430,390)	(365,711)
Standardized measure of discounted future net cash flows	$ 862,649	$ 603,015	$ 554,972	$ 1,143,094
Discount for estimated timing of cash flows	10.00%	10.00%	10.00%
Noncontrolling Interest
Discounted Future Net Cash Flows Relating To Proved Oil And Gas Reserves [Line Items]
Standardized measure of discounted future net cash flows	$ 500	$ 600	$ 700