Earnings from Equity Investments (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Condensed Financial Statements, Captions [Line Items]
Earnings from equity investments	$ 10,434		$ 11,363		$ 12,531
Muskegon Pipeline LLC
Condensed Financial Statements, Captions [Line Items]
Earnings from equity investments	958		1,482		1,437
Transport4, LLC
Condensed Financial Statements, Captions [Line Items]
Earnings from equity investments	185		162		147
West Shore Pipe Line Company
Condensed Financial Statements, Captions [Line Items]
Earnings from equity investments	6,605	[1]	4,988	[1]	4,809	[1]
West Texas LPG Pipeline Limited Partnership
Condensed Financial Statements, Captions [Line Items]
Earnings from equity investments	2,297	[2]	4,731	[2]	6,138	[2]
South Portland Terminal LLC
Condensed Financial Statements, Captions [Line Items]
Earnings from equity investments	$ 389	[3]

[1] In August 2010, we acquired additional shares, which increased our interest from 24.9% to 34.6%. See Note 3 for further information.

[2] In May 2011, we sold our 20.0% interest. See Note 3 for further information.

[3] In July 2011, we acquired a 50.0% interest. See Note 3 for further information.