Disposal of long-lived assets (Details) $ in Millions, $ in Millions					9 Months Ended
	Feb. 25, 2019 USD ($)	Feb. 25, 2019 CAD ($)	Apr. 12, 2018 USD ($)	Mar. 15, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jul. 30, 2019 USD ($)	Jul. 17, 2019 USD ($)
Disposal of long-lived assets [Line Items]
Other Asset Impairment Charges					$ 3.4
South Texas crude oil trucking assets [Member]
Disposal of long-lived assets [Line Items]
Disposal Group, Including Discontinued Operation, Consideration							$ 5.5
Sherman, Texas Assets [Member] [Domain]
Disposal of long-lived assets [Line Items]
Disposal Group, Including Discontinued Operation, Consideration								$ 5.3
Impairment of Long-Lived Assets to be Disposed of					$ 5.2
Sem Logistics [Member]
Disposal of long-lived assets [Line Items]
Proceeds from Divestiture of Businesses			$ 73.1
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal						$ 0.4
Income (loss) from disposal, excluding discontinued operations, before tax, excluding gain/loss on disposal						5.4
SemMexico [Member]
Disposal of long-lived assets [Line Items]
Proceeds from Divestiture of Businesses				$ 70.7
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal						1.6
Income (loss) from disposal, excluding discontinued operations, before tax, excluding gain/loss on disposal						$ 2.3
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	$ 490.8	$ 645.6