Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Midstream Services — Affiliate	$ 91,996	$ 64,263
Total Revenues	147,960	97,733
Income (Loss) Before Income Taxes	63,362	39,210
Additions to Long-Lived Assets	75,358	455,021
Additions to Investments	270,603	0
Total Assets	2,322,462		$ 1,997,917
Gathering Systems
Segment Reporting Information [Line Items]
Midstream Services — Affiliate	64,409	43,979
Total Revenues	116,564	73,547
Income (Loss) Before Income Taxes	47,586	30,827
Additions to Long-Lived Assets	72,333	447,389
Additions to Investments	0
Total Assets	1,851,930		1,804,100
Fresh Water Delivery
Segment Reporting Information [Line Items]
Midstream Services — Affiliate	27,587	20,284
Total Revenues	31,396	24,186
Income (Loss) Before Income Taxes	23,209	17,503
Additions to Long-Lived Assets	2,756	7,632
Additions to Investments	0
Total Assets	109,758		96,280
Investments in Midstream Entities
Segment Reporting Information [Line Items]
Midstream Services — Affiliate	0	0
Total Revenues	0	0
Income (Loss) Before Income Taxes	2,341	2,868
Additions to Long-Lived Assets	0	0
Additions to Investments	270,603
Total Assets	346,998		82,317
Corporate
Segment Reporting Information [Line Items]
Midstream Services — Affiliate	0	0
Total Revenues	0	0
Income (Loss) Before Income Taxes	(9,774)	(11,988)
Additions to Long-Lived Assets	269	0
Additions to Investments	0
Total Assets	13,776		$ 15,220
Midstream Services — Third Party
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	23,094	11,360
Midstream Services — Third Party | Gathering Systems
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	19,285	7,458
Midstream Services — Third Party | Fresh Water Delivery
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	3,809	3,902
Midstream Services — Third Party | Investments in Midstream Entities
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	0	0
Midstream Services — Third Party | Corporate
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	0	0
Crude Oil Sales — Third Party
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	32,870	22,110
Crude Oil Sales — Third Party | Gathering Systems
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	32,870	22,110
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 in Midstream Entities
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	0	0
Crude Oil Sales — Third Party | Corporate
Segment Reporting Information [Line Items]
Services and Sales Revenues - Third Party	$ 0	$ 0