Acquisition (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Jan. 03, 2012
Business Acquisition [Line Items]
Purchase price, net of post-closing adjustments of acquired entity	205.6
Number of small offshore pipelines acquired		2
Gulf Of Mexico Crude Oil Pipeline Systems [Member]
Business Acquisition [Line Items]
Effective date of acquisition	January 1, 2012
Purchase price, net of post-closing adjustments of acquired entity		$ 205.6
Genesis Energy Interest In Poseidon Oil Pipeline Company LLC [Member]
Business Acquisition [Line Items]
Percentage of equity interest acquired		28.00%
Genesis Energy Interest In Odyssey LLC [Member]
Business Acquisition [Line Items]
Percentage of equity interest acquired		29.00%
Genesis Energy Interest In Marathon Offshore Pipeline LLC, Subsequently Named GOPL [Member]
Business Acquisition [Line Items]
Percentage of equity interest acquired		100.00%
GOPL Interest In Eugene Island Crude Oil Pipeline System [Member]
Business Acquisition [Line Items]
Percentage of equity interest acquired		23.00%
GOPL Interest In Two Small Offshore Pipelines [Member] | Other Offshore Pipelines [Member]
Business Acquisition [Line Items]
Percentage of equity interest acquired		100.00%
Poseidon Oil Pipeline Company, L.L.C. [Member]
Business Acquisition [Line Items]
Pipeline capacity, barrels per day	400,000
Pipeline length, in miles	367
Odyssey Pipeline L.L.C. [Member]
Business Acquisition [Line Items]
Pipeline capacity, barrels per day	300,000
Pipeline length, in miles	120
GOPL [Member]
Business Acquisition [Line Items]
Pipeline capacity, barrels per day	200,000
Pipeline length, in miles	183
Pipeline diameter, in inches	20
Minimum [Member] | Poseidon Oil Pipeline Company, L.L.C. [Member]
Business Acquisition [Line Items]
Pipeline diameter, in inches	16
Minimum [Member] | Odyssey Pipeline L.L.C. [Member]
Business Acquisition [Line Items]
Pipeline diameter, in inches	12
Maximum [Member] | Poseidon Oil Pipeline Company, L.L.C. [Member]
Business Acquisition [Line Items]
Pipeline diameter, in inches	24
Maximum [Member] | Odyssey Pipeline L.L.C. [Member]
Business Acquisition [Line Items]
Pipeline diameter, in inches	20