Disposals of Long-Lived Assets Disposals of Long-Lived Assets (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement [Line Items]
Other Asset Impairment Charges									$ 3,727
Loss (gain) on disposal or impairment	$ (30,468)	$ 41,625	$ (234)	$ 2,410	$ 38	$ 1,018	$ 1,685	$ 13,307	13,333	$ 16,048	$ 11,472
Sem Logistics [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Statement [Line Items]
Impairment of Long-Lived Assets to be Disposed of	76,700								76,661
SemMexico [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Statement [Line Items]
Impairment of Long-Lived Assets to be Disposed of	13,500								13,511
SemGas [Member]
Statement [Line Items]
Other Asset Impairment Charges									30,985
Goodwill, Impairment Loss										$ 13,052
Crude Transportation [Member]
Statement [Line Items]
Goodwill, Impairment Loss		$ 26,600							26,628		$ 9,488
Impairment of Intangible Assets, Finite-lived	12,100								12,087
Glass Mountain Pipeline Llc [Member]
Statement [Line Items]
Equity Method Investment, Realized Gain on Disposal	$ (150,300)								$ (150,266)