Equity Investments - Equity Investments Table (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	[1]	Sep. 30, 2019	Sep. 30, 2018	[1]
Schedule of Equity Method Investments [Line Items]
Balance	[1]				$ 1,092,088
Acquisitions					92,546
Equity income, net		$ 53,893	$ 54,215		175,483	$ 133,874
Contributions					108,118	67,085
Distributions					(182,337)	(125,834)
Distributions in excess of cumulative earnings					(21,203)	$ (19,816)
Balance		1,264,695			1,264,695
Fort Union [Member]
Schedule of Equity Method Investments [Line Items]
Balance					2,259
Acquisitions					0
Equity income, net					(1,698)
Contributions					0
Distributions					0
Distributions in excess of cumulative earnings					(565)
Balance		(4)			(4)
White Cliffs [Member]
Schedule of Equity Method Investments [Line Items]
Balance					43,020
Acquisitions					0
Equity income, net					7,720
Contributions					4,992
Distributions					(7,283)
Distributions in excess of cumulative earnings					(2,822)
Balance		45,627			45,627
Rendezvous [Member]
Schedule of Equity Method Investments [Line Items]
Balance					37,841
Acquisitions					0
Equity income, net					595
Contributions					0
Distributions					(2,051)
Distributions in excess of cumulative earnings					(1,805)
Balance		34,580			34,580
Mont Belvieu JV [Member]
Schedule of Equity Method Investments [Line Items]
Balance					104,949
Acquisitions					0
Equity income, net					21,755
Contributions					0
Distributions					(21,784)
Distributions in excess of cumulative earnings					(1,391)
Balance		103,529			103,529
Texas Express Gathering [Member]
Schedule of Equity Method Investments [Line Items]
Balance					19,358
Acquisitions					0
Equity income, net					3,000
Contributions					0
Distributions					(3,017)
Distributions in excess of cumulative earnings					(558)
Balance		18,783			18,783
Texas Express Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Balance					193,198
Acquisitions					0
Equity income, net					22,747
Contributions					11,020
Distributions					(24,677)
Distributions in excess of cumulative earnings					0
Balance		202,288			202,288
Front Range Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Balance					176,436
Acquisitions					0
Equity income, net					23,494
Contributions					20,175
Distributions					(23,619)
Distributions in excess of cumulative earnings					0
Balance		196,486			196,486
Whitethorn LLC [Member]
Schedule of Equity Method Investments [Line Items]
Balance					161,858
Acquisitions					0
Equity income, net					62,893
Contributions					10,332
Distributions					(62,034)
Distributions in excess of cumulative earnings					(7,139)
Balance		165,910			165,910
Cactus II [Member]
Schedule of Equity Method Investments [Line Items]
Balance					106,360
Acquisitions					0
Equity income, net					0
Contributions					47,599
Distributions					0
Distributions in excess of cumulative earnings					0
Balance		153,959			153,959
Capitalized interest					4,800
Saddlehorn [Member]
Schedule of Equity Method Investments [Line Items]
Balance					108,507
Acquisitions					0
Equity income, net					18,408
Contributions					3,550
Distributions					(17,679)
Distributions in excess of cumulative earnings					0
Balance		112,786			112,786
Panola [Member]
Schedule of Equity Method Investments [Line Items]
Balance					22,769
Acquisitions					0
Equity income, net					1,492
Contributions					0
Distributions					(1,492)
Distributions in excess of cumulative earnings					(861)
Balance		21,908			21,908
Mi Vida [Member]
Schedule of Equity Method Investments [Line Items]
Balance					64,631
Acquisitions					0
Equity income, net					8,469
Contributions					0
Distributions					(10,611)
Distributions in excess of cumulative earnings					(2,743)
Balance		59,746			59,746
Ranch Westex [Member]
Schedule of Equity Method Investments [Line Items]
Balance					50,902
Acquisitions					0
Equity income, net					5,187
Contributions					0
Distributions					(6,668)
Distributions in excess of cumulative earnings					(2,508)
Balance		46,913			46,913
Red Bluff Express [Member]
Schedule of Equity Method Investments [Line Items]
Balance					0
Acquisitions					92,546
Equity income, net					1,421
Contributions					10,450
Distributions					(1,422)
Distributions in excess of cumulative earnings					(811)
Balance		$ 102,184			$ 102,184

[1] Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.