Segment Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) segment	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Revenues	$ 234,382	$ 212,426	$ 450,720	$ 397,448
Number of segments | segment			2
Realized gain (loss) on derivatives	1,165	(2,488)	$ 4,435	(6,746)
Unrealized gain (loss) on derivatives	6,157	1,429	(39,562)	11,845
Expenses	164,915	137,374	331,264	255,192
Operating (loss) income	76,789	73,993	84,329	147,355
Total assets	3,751,451	2,555,847	3,751,451	2,555,847	$ 3,455,518
Capital expenditures	209,639	232,977	437,488	468,665
Depletion, depreciation and amortization	80,132	66,838	156,999	122,207
Corporate
Segment Reporting Information [Line Items]
Realized gain (loss) on derivatives	0	0	0	0
Unrealized gain (loss) on derivatives	0	0	0	0
Expenses	17,783	18,475	34,734	35,684
Operating (loss) income	(17,783)	(18,475)	(34,734)	(35,684)
Total assets	87,800	143,332	87,800	143,332
Capital expenditures	1,400	732	2,206	1,258
Depletion, depreciation and amortization	600	25,000	1,200	600
Consolidations and Eliminations
Segment Reporting Information [Line Items]
Realized gain (loss) on derivatives	0	0	0	0
Unrealized gain (loss) on derivatives	0	0	0	0
Expenses	(17,807)	(16,489)	(36,223)	(29,233)
Operating (loss) income	0	0	0	0
Total assets	0	0	0	0
Capital expenditures	0	0	0	0
Exploration and Production | Operating Segments
Segment Reporting Information [Line Items]
Realized gain (loss) on derivatives	1,165	(2,488)	4,435	(6,746)
Unrealized gain (loss) on derivatives	6,157	1,429	(39,562)	11,845
Expenses	141,514	126,025	283,493	232,180
Operating (loss) income	75,371	80,145	82,606	160,408
Total assets	3,155,577	2,058,447	3,155,577	2,058,447
Capital expenditures	166,532	199,345	364,143	388,790
Depletion, depreciation and amortization	75,700	64,500	148,300	117,800
Midstream | Operating Segments
Segment Reporting Information [Line Items]
Realized gain (loss) on derivatives	0	0	0	0
Unrealized gain (loss) on derivatives	0	0	0	0
Expenses	23,425	9,363	49,260	16,561
Operating (loss) income	19,201	12,323	36,457	22,631
Total assets	508,074	354,068	508,074	354,068
Capital expenditures	41,707	32,900	71,139	78,617
Depletion, depreciation and amortization	3,800	2,300	7,500	3,900
Net income attributable to non-controlling interest in subsidiaries		(5,800)
Capital expenditures attributable to non-controlling interest	24,200	16,100	37,900
Capital expenditures attributable to land and seismic acquisition expenditures	8,200		31,300	38,500
Operating Income (Loss) | Midstream | Operating Segments
Segment Reporting Information [Line Items]
Net income attributable to non-controlling interest in subsidiaries	(8,300)		(15,800)	(10,900)
Oil and natural gas revenues
Segment Reporting Information [Line Items]
Revenues	211,060	209,019	404,329	390,973
Oil and natural gas revenues | Corporate
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Oil and natural gas revenues | Consolidations and Eliminations
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Oil and natural gas revenues | Exploration and Production | Operating Segments
Segment Reporting Information [Line Items]
Revenues	209,563	207,229	401,226	387,489
Oil and natural gas revenues | Midstream | Operating Segments
Segment Reporting Information [Line Items]
Revenues	1,497	1,790	3,103	3,484
Third-party midstream services revenues
Segment Reporting Information [Line Items]
Revenues	14,359	3,407	26,197	6,475
Third-party midstream services revenues | Corporate
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Third-party midstream services revenues | Consolidations and Eliminations
Segment Reporting Information [Line Items]
Revenues	(17,807)	(16,489)	(36,223)	(29,233)
Third-party midstream services revenues | Exploration and Production | Operating Segments
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Third-party midstream services revenues | Midstream | Operating Segments
Segment Reporting Information [Line Items]
Revenues	32,166	19,896	62,420	35,708
Sales of purchased natural gas
Segment Reporting Information [Line Items]
Revenues	8,963	$ 0	20,194	$ 0
Sales of purchased natural gas | Corporate
Segment Reporting Information [Line Items]
Revenues	0		0
Sales of purchased natural gas | Consolidations and Eliminations
Segment Reporting Information [Line Items]
Revenues	0		0
Sales of purchased natural gas | Exploration and Production | Operating Segments
Segment Reporting Information [Line Items]
Revenues	0		0
Sales of purchased natural gas | Midstream | Operating Segments
Segment Reporting Information [Line Items]
Revenues	$ 8,963		$ 20,194