Amounts Recognized in Consolidated Balance Sheets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
RIGP
Liabilities:
Accrued employee benefit liabilities-noncurrent	$ 14,673	$ 13,152
AOCI:
Net actuarial loss	11,160	9,829
Total	11,160	9,829
Retiree Medical Plan
Liabilities:
Accrued employee benefit liabilities-current	3,071	3,817
Accrued employee benefit liabilities-noncurrent	35,926	36,018
AOCI:
Net actuarial loss	13,078	15,103
Prior service credit	(4,353)	(7,318)
Total	$ 8,725	$ 7,785