Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Midstream Services — Affiliate	$ 73,136	$ 56,755	$ 204,323	$ 161,186
Total Revenues	139,163	63,111	358,867	171,208
Income (Loss) Before Income Taxes	48,609	43,789	132,444	117,416
Total Assets	1,959,462		1,959,462		$ 829,758
Gathering Systems
Segment Reporting Information [Line Items]
Midstream Services — Affiliate	55,720	39,166	147,549	102,930
Total Revenues	115,818	40,740	289,161	104,504
Income (Loss) Before Income Taxes	34,780	28,307	94,674	70,633
Total Assets	1,711,828		1,711,828		593,590
Fresh Water Delivery
Segment Reporting Information [Line Items]
Midstream Services — Affiliate	17,416	17,589	56,774	58,256
Total Revenues	23,345	22,371	69,706	66,704
Income (Loss) Before Income Taxes	18,129	17,823	54,066	53,298
Total Assets	85,030		85,030		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	(4,300)	(2,341)	(16,296)	(6,515)
Total Assets	162,604		162,604		$ 167,990
Midstream Services — Third Party
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	19,934	6,356	44,763	10,022
Midstream Services — Third Party | Gathering Systems
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	14,005	1,574	31,831	1,574
Midstream Services — Third Party | Fresh Water Delivery
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	5,929	4,782	12,932	8,448
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	46,093	$ 0	109,781	$ 0
Crude Oil Sales — Third Party | Gathering Systems
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	46,093		109,781
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