Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Midstream Services — Affiliate	$ 66,924	$ 54,117	$ 131,187	$ 104,431
Total Revenues	121,971	57,783	219,704	108,097
Income (Loss) Before Income Taxes	44,625	39,107	83,835	73,627
Total Assets	1,864,465		1,864,465		$ 829,758
Gathering Systems
Segment Reporting Information [Line Items]
Midstream Services — Affiliate	47,850	33,769	91,829	63,764
Total Revenues	99,796	33,769	173,343	63,764
Income (Loss) Before Income Taxes	29,066	22,343	59,894	42,326
Total Assets	1,625,130		1,625,130		593,590
Fresh Water Delivery
Segment Reporting Information [Line Items]
Midstream Services — Affiliate	19,074	20,348	39,358	40,667
Total Revenues	22,175	24,014	46,361	44,333
Income (Loss) Before Income Taxes	18,434	18,872	35,937	35,475
Total Assets	79,574		79,574		68,178
Investments and Other
Segment Reporting Information [Line Items]
Midstream Services — Affiliate	0	0	0	0
Total Revenues	0	0	0	0
Income (Loss) Before Income Taxes	(2,875)	(2,108)	(11,996)	(4,174)
Total Assets	159,761		159,761		$ 167,990
Midstream Services — Third Party
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	13,469	3,666	24,829	3,666
Midstream Services — Third Party | Gathering Systems
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	10,368	0	17,826	0
Midstream Services — Third Party | Fresh Water Delivery
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	3,101	3,666	7,003	3,666
Midstream Services — Third Party | Investments and Other
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	0	0	0	0
Crude Oil Sales — Third Party
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	41,578	$ 0	63,688	$ 0
Crude Oil Sales — Third Party | Gathering Systems
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	41,578		63,688
Crude Oil Sales — Third Party | Fresh Water Delivery
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	0		0
Crude Oil Sales — Third Party | Investments and Other
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	$ 0		$ 0