Segment Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) segment	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Revenues	$ 216,338	$ 185,022
Number of segments | segment	2
Realized gain (loss) on derivatives	$ 3,270	(4,258)
Unrealized (loss) gain on derivatives	(45,719)	10,416
Expenses	166,348	117,818
Operating (loss) income	7,541	73,362
Total assets	3,583,298	2,275,705	$ 3,455,518
Capital expenditures	227,850	235,688
Depletion, depreciation and amortization	76,866	55,369
Impairment charges		0
Other (expense) income	(110)	53
Income before income taxes	(9,485)	64,924
Corporate
Segment Reporting Information [Line Items]
Realized gain (loss) on derivatives		0
Unrealized (loss) gain on derivatives		0
Expenses	16,950	17,209
Operating (loss) income	(16,950)	(17,209)
Total assets	62,087	50,018
Capital expenditures	807	526
Depletion, depreciation and amortization	600	600
Consolidations and Eliminations
Segment Reporting Information [Line Items]
Realized gain (loss) on derivatives		0
Unrealized (loss) gain on derivatives		0
Expenses	(18,416)	(12,744)
Total assets	0	0
Capital expenditures	0	0
Exploration and Production | Operating Segments
Segment Reporting Information [Line Items]
Realized gain (loss) on derivatives	3,270	(4,258)
Unrealized (loss) gain on derivatives	(45,719)	10,416
Expenses	141,980	106,155
Operating (loss) income	7,234	80,263
Total assets	3,043,375	1,902,151
Capital expenditures	197,611	189,445
Depletion, depreciation and amortization	72,600	53,200
Midstream | Operating Segments
Segment Reporting Information [Line Items]
Realized gain (loss) on derivatives		0
Unrealized (loss) gain on derivatives		0
Expenses	25,834	7,198
Operating (loss) income	17,257	10,308
Total assets	477,836	323,536
Capital expenditures	29,432	45,717
Depletion, depreciation and amortization	3,700	1,500
Net income attributable to non-controlling interest in subsidiaries		(5,000)
Capital expenditures attributable to non-controlling interest	13,700	22,400
Capital expenditures attributable to land and seismic acquisition expenditures	23,100
Operating Income (Loss) | Midstream | Operating Segments
Segment Reporting Information [Line Items]
Net income attributable to non-controlling interest in subsidiaries	(7,500)
Oil and natural gas revenues
Segment Reporting Information [Line Items]
Revenues	193,269	181,954
Oil and natural gas revenues | Exploration and Production | Operating Segments
Segment Reporting Information [Line Items]
Revenues	191,663	180,260
Oil and natural gas revenues | Midstream | Operating Segments
Segment Reporting Information [Line Items]
Revenues	1,606	1,694
Third-party midstream services revenues
Segment Reporting Information [Line Items]
Revenues	11,838	3,068
Third-party midstream services revenues | Corporate
Segment Reporting Information [Line Items]
Revenues	0	0
Third-party midstream services revenues | Consolidations and Eliminations
Segment Reporting Information [Line Items]
Revenues	(18,416)	(12,744)
Third-party midstream services revenues | Exploration and Production | Operating Segments
Segment Reporting Information [Line Items]
Revenues	0	0
Third-party midstream services revenues | Midstream | Operating Segments
Segment Reporting Information [Line Items]
Revenues	30,254	15,812
Sales of purchased natural gas
Segment Reporting Information [Line Items]
Revenues	11,231	$ 0
Sales of purchased natural gas | Corporate
Segment Reporting Information [Line Items]
Revenues	0
Sales of purchased natural gas | Consolidations and Eliminations
Segment Reporting Information [Line Items]
Revenues	0
Sales of purchased natural gas | Exploration and Production | Operating Segments
Segment Reporting Information [Line Items]
Revenues	0
Sales of purchased natural gas | Midstream | Operating Segments
Segment Reporting Information [Line Items]
Revenues	$ 11,231