Disposals of Long-Lived Assets (Details Textual) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 23, 2018	Jan. 05, 2018
Current assets held for sale	$ 38,063	$ 38,063	$ 0
Current liabilities held for sale	23,847	23,847	0
Other Asset Impairment Charges		3,727
Proceeds from sale of equity method investment and other long-lived assets		314,821	$ 151	$ 3,688
SemGas [Member]
Other Asset Impairment Charges		30,985
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | SemMexico [Member]
Impairment of Long-Lived Assets to be Disposed of	13,500	13,511
Disposal Group, Including Discontinued Operation, Foreign Currency Translation Gains (Losses)		(30,900)
Disposal Group, Including Discontinued Operation, Pre Tax Income (Loss)		(8,200)
Disposal Group, Including Discontinued Operation, Property, Plant and Equipment	29,400	29,400
Current assets held for sale	34,900	34,900
Current liabilities held for sale	19,400	19,400
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Sem Logistics [Member]
Impairment of Long-Lived Assets to be Disposed of	76,700	76,661
Disposal Group, Including Discontinued Operation, Foreign Currency Translation Gains (Losses)		(22,800)
Disposal Group, Including Discontinued Operations, Net Realizable Value	71,500	71,500
Disposal Group, Including Discontinued Operation, Pre Tax Income (Loss)		(73,000)
Disposal Group, Including Discontinued Operation, Property, Plant and Equipment	136,800	136,800
Current assets held for sale	3,100	3,100
Current liabilities held for sale	$ 4,400	$ 4,400
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Kansas gas gathering and compression assets [Member] | SemGas [Member]
Gain (loss) on disposal				(1,700)
Proceeds from sale of equity method investment and other long-lived assets				$ 1,000
Subsequent Event [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | SemMexico [Member]
Disposal Group, Including Discontinued Operation, Consideration						$ 55,000
Subsequent Event [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Sem Logistics [Member]
Disposal Group, Including Discontinued Operation, Consideration					$ 71,500