Segment Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of segments | segment			2
Oil and natural gas revenues	$ 209,019	$ 113,764	$ 390,973	$ 228,611
Third-party midstream services revenues	3,407	2,099	6,475	3,654
Realized (loss) gain on derivatives	(2,488)	558	(6,746)	(1,661)
Unrealized gain on derivatives	1,429	13,190	11,845	33,821
Expenses	137,374	90,622	255,192	171,157
Operating (loss) income	73,993	38,989	147,355	93,268
Total assets	2,555,847	1,777,076	2,555,847	1,777,076	$ 2,145,690
Capital expenditures	232,977	194,682	468,665	417,399
Depletion, depreciation and amortization	66,838	41,274	122,207	75,266
Impairment charges		0	0
Other (expense) income	(352)	1,922	(299)	1,991
Income Tax Expense (Benefit)		0		0
Income before income taxes	65,637	31,687	130,561	77,587
Net Income (Loss) Attributable to Parent	59,806	28,509	119,700	72,493
Corporate
Segment Reporting Information [Line Items]
Oil and natural gas revenues		0
Third-party midstream services revenues	0	0	0	0
Realized (loss) gain on derivatives		0
Unrealized gain on derivatives		0
Expenses	18,475	15,852	35,684	31,608
Operating (loss) income	(18,475)	(15,852)	(35,684)	(31,608)
Total assets	143,332	147,509	143,332	147,509
Capital expenditures	732	1,752	1,258	3,216
Depletion, depreciation and amortization	0	400	600	700
Consolidations and Eliminations
Segment Reporting Information [Line Items]
Oil and natural gas revenues		0
Third-party midstream services revenues	(16,489)	(9,268)	(29,233)	(17,329)
Realized (loss) gain on derivatives		0
Unrealized gain on derivatives		0
Expenses	(16,489)	(9,268)	(29,233)	(17,329)
Total assets	0	0	0	0
Capital expenditures	0	0	0	0
Exploration and Production | Operating Segments
Segment Reporting Information [Line Items]
Oil and natural gas revenues	207,229	113,387	387,489	227,552
Third-party midstream services revenues	0	0	0	0
Realized (loss) gain on derivatives	(2,488)	558	(6,746)	(1,661)
Unrealized gain on derivatives	1,429	13,190	11,845	33,821
Expenses	126,025	78,078	232,180	146,416
Operating (loss) income	80,145	49,057	160,408	113,296
Total assets	2,058,447	1,436,678	2,058,447	1,436,678
Capital expenditures	199,345	165,583	388,790	373,956
Depletion, depreciation and amortization	64,500	39,600	117,800	72,100
Midstream | Operating Segments
Segment Reporting Information [Line Items]
Oil and natural gas revenues	1,790	377	3,484	1,059
Third-party midstream services revenues	19,896	11,367	35,708	20,983
Realized (loss) gain on derivatives		0
Unrealized gain on derivatives		0
Expenses	9,363	5,960	16,561	10,462
Operating (loss) income	12,323	5,784	22,631	11,580
Total assets	354,068	192,889	354,068	192,889
Capital expenditures	32,900	27,347	78,617	40,227
Depletion, depreciation and amortization	2,300	1,300	3,900	2,500
Net income attributable to non-controlling interest in subsidiaries		(3,200)	(10,900)	(5,100)
Capital expenditures	16,100	$ 13,400	$ 38,500	$ 18,600
Operating Income (Loss) | Midstream | Operating Segments
Segment Reporting Information [Line Items]
Net income attributable to non-controlling interest in subsidiaries	$ (5,800)