Acquisitions - Schedule of preliminary fair values of assets acquired and liabilities assumed (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Business Acquisition [Line Items]
Net working capital	$ 1,700
Goodwill	8,407	5,636
Rogers [Member]
Business Acquisition [Line Items]
Property and equipment	18,810
Net assets acquired	19,955
Rogers [Member] | Wholesale Fuel Distribution Rights [Member]
Business Acquisition [Line Items]
Intangible assets	1,145
Rocky Top [Member]
Business Acquisition [Line Items]
Property and equipment	33,670
Net assets acquired	36,850
Rocky Top [Member] | Wholesale Fuel Distribution Rights [Member]
Business Acquisition [Line Items]
Intangible assets	3,180
Dunmore [Member]
Business Acquisition [Line Items]
Property and equipment	22,800
Intangible assets	5,800
Total identifiable assets	28,600
Net identifiable assets acquired	28,400
Goodwill	600
Net assets acquired	29,000
Dunmore [Member] | Original Preliminary Purchase Price Allocation [Member]
Business Acquisition [Line Items]
Property and equipment	20,400
Intangible assets	8,200
Total identifiable assets	28,600
Net identifiable assets acquired	28,400
Goodwill	600
Net assets acquired	29,000
Dunmore [Member] | Cumulative Adjustments [Member]
Business Acquisition [Line Items]
Property and equipment	2,400
Intangible assets	(2,400)
Dunmore [Member] | Lease Agreements With Above Average Market Value [Member]
Business Acquisition [Line Items]
Other liabilities	200
Dunmore [Member] | Lease Agreements With Above Average Market Value [Member] | Original Preliminary Purchase Price Allocation [Member]
Business Acquisition [Line Items]
Other liabilities	200
Express Lane [Member]
Business Acquisition [Line Items]
Net working capital	1,720
Property and equipment	28,645
Intangible assets	19,700
Environmental indemnification asset	1,177
Total identifiable assets	51,242
Environmental liabilities	1,177
Other liabilities	8,616
Total identifiable liabilities	9,793
Net identifiable assets acquired	41,449
Goodwill	3,764
Net assets acquired	45,213
Express Lane [Member] | Original Preliminary Purchase Price Allocation [Member]
Business Acquisition [Line Items]
Net working capital	1,822
Property and equipment	27,500
Intangible assets	17,600
Environmental indemnification asset	1,177
Total identifiable assets	48,099
Environmental liabilities	1,177
Other liabilities	2,500
Total identifiable liabilities	3,677
Net identifiable assets acquired	44,422
Goodwill	993
Net assets acquired	45,415
Express Lane [Member] | Cumulative Adjustments [Member]
Business Acquisition [Line Items]
Net working capital	(102)
Property and equipment	1,145
Intangible assets	2,100
Total identifiable assets	3,143
Other liabilities	6,116
Total identifiable liabilities	6,116
Net identifiable assets acquired	(2,973)
Goodwill	2,771
Net assets acquired	$ (202)