Disposals of Long-Lived Assets (Details Textual) - USD ($) $ in Thousands			3 Months Ended	12 Months Ended
	Apr. 12, 2018	Mar. 15, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current assets held for sale			$ 38,063	$ 0	$ 38,063
Current liabilities held for sale			23,847	0	23,847
Other Asset Impairment Charges					3,727	$ 0
SemGas [Member]
Other Asset Impairment Charges					30,985
Sem Mexico [Member]
Proceeds from Divestiture of Businesses		$ 70,700
Gain (loss) on disposal				1,600
Income (loss) from disposal, excluding discontinued operations, before tax, excluding gain/loss on disposal				2,300
Sem Logistics [Member]
Proceeds from Divestiture of Businesses	$ 73,100
Gain (loss) on disposal				400
Income (loss) from disposal, excluding discontinued operations, before tax, excluding gain/loss on disposal				$ 5,400
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Sem Mexico [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 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