Significant Accounting Policies - Additional Information (Details) - gal gal in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Significant Accounting Policies [Line Items]
Purchases Under Supply Agreements Volume	928.0	869.6	884.6
Valero Energy Corporation [Member]
Significant Accounting Policies [Line Items]
Purchases Under Supply Agreements Volume	1,700.0	1,800.0	1,900.0
Wholesale Distribution Volumes [Member] | DMS [Member] | Sales Revenue, Net [Member]
Significant Accounting Policies [Line Items]
Concentration Risk, Percentage	13.00%	16.00%	17.00%
Wholesale Distribution Volumes [Member] | CST Brands Inc. [Member] | Sales Revenue, Net [Member]
Significant Accounting Policies [Line Items]
Concentration Risk, Percentage	8.00%	8.00%	7.00%
Rental Income [Member] | DMS [Member] | Sales Revenue, Net [Member]
Significant Accounting Policies [Line Items]
Concentration Risk, Percentage	22.00%	26.00%	36.00%
Rental Income [Member] | CST Brands Inc. [Member] | Sales Revenue, Net [Member]
Significant Accounting Policies [Line Items]
Concentration Risk, Percentage	20.00%	21.00%	17.00%
Supplier Concentration Risk [Member] | Purchases Net [Member] | ExxonMobil, Corp [Member]
Significant Accounting Policies [Line Items]
Concentration Risk, Percentage	28.00%	30.00%	30.00%
Supplier Concentration Risk [Member] | Purchases Net [Member] | BP P.L.C [Member]
Significant Accounting Policies [Line Items]
Concentration Risk, Percentage	27.00%	25.00%	26.00%
Supplier Concentration Risk [Member] | Purchases Net [Member] | Motiva (Shell) [Member]
Significant Accounting Policies [Line Items]
Concentration Risk, Percentage	16.00%	24.00%	26.00%
Supplier Concentration Risk [Member] | Purchases Net [Member] | Other suppliers [Member]
Significant Accounting Policies [Line Items]
Concentration Risk, Percentage	10.00%	10.00%	10.00%
Accounting Standards Update 2014-09
Significant Accounting Policies [Line Items]
Percentage effect on revenue	90.00%
Distribution Rights [Member]
Significant Accounting Policies [Line Items]
Finite-Lived Intangible Asset, Useful Life	10 years
Covenant Not to Compete [Member]
Significant Accounting Policies [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years
Building and Building Improvements [Member] | Minimum [Member]
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Building and Building Improvements [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Equipment | Minimum [Member]
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Equipment | Maximum [Member]
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	30 years
Leasehold Improvements [Member] | Minimum [Member]
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	7 years
Leasehold Improvements [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	10 years