Commitments and Contingencies (Details Textual) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
Commitments and Contingencies (Textual) [Abstract]
Site contingency number of sites checked	6
Sites in various stages of follow-up	4
Sites with limited soil and ground water impact	2
Sites requiring additional investigation	2
Minimum [Member]
Commitments and Contingencies (Textual) [Abstract]
Notice required to cancel purchase agreements, days	30 days
Maximum [Member]
Commitments and Contingencies (Textual) [Abstract]
Notice required to cancel purchase agreements, days	120 days
Crude Transportation [Member]
Commitments and Contingencies (Textual) [Abstract]
Site contingency number of sites checked	5
SemGas [Member]
Commitments and Contingencies (Textual) [Abstract]
Site contingency number of sites checked	1
SemCAMS [Member]
Commitments and Contingencies (Textual) [Abstract]
Asset retirement obligation liability	$ 22.7
Estimated cost to retire facilities	$ 129.0