Disposal of long-lived assets (Details) $ in Thousands, $ in Millions					6 Months Ended
	Feb. 25, 2019 USD ($)	Feb. 25, 2019 CAD ($)	Apr. 12, 2018 USD ($)	Mar. 15, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Disposal of long-lived assets [Line Items]
Disposal Group, Including Discontinued Operation, Assets, Current					$ 1,025		$ 0
Disposal Group, Including Discontinued Operation, Liabilities, Current					1,935		$ 0
Other Asset Impairment Charges					3,400
Sherman, Texas Assets [Member] [Domain]
Disposal of long-lived assets [Line Items]
Disposal Group, Including Discontinued Operation, Consideration					5,300
Impairment of Long-Lived Assets to be Disposed of					5,200
Disposal Group, Including Discontinued Operation, Property, Plant and Equipment					5,500
Disposal Group, Including Discontinued Operation, Assets, Current					1,000
Disposal Group, Including Discontinued Operation, Liabilities, Current					$ 1,900
Sem Logistics [Member]
Disposal of long-lived assets [Line Items]
Proceeds from Divestiture of Businesses			$ 73,100
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal						$ 400
Income (loss) from disposal, excluding discontinued operations, before tax, excluding gain/loss on disposal						5,400
SemMexico [Member]
Disposal of long-lived assets [Line Items]
Proceeds from Divestiture of Businesses				$ 70,700
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal						1,600
Income (loss) from disposal, excluding discontinued operations, before tax, excluding gain/loss on disposal						$ 2,300
SemCAMS Midstream [Member]
Disposal of long-lived assets [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired					51.00%
Semcams [Member]
Disposal of long-lived assets [Line Items]
Equity contributed to joint venture	100.00%	100.00%
Proceeds from Divestiture of Businesses	$ 490,800	$ 645.6