Accumulated Benefit Obligation in Excess of Plan Assets for the RIGP (Detail) (RIGP, USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
RIGP
Pension and Other Postretirement Benefits Disclosure [Line Items]
Projected benefit obligation	$ 21,291	$ 17,959
Accumulated benefit obligation	14,687	11,119
Fair value of plan assets	$ 6,618	$ 4,807

If aggregate disclosures are presented, the aggregate pension accumulated benefit obligation for pension plans with accumulated benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.

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If aggregate disclosures are presented, the aggregate fair value of plan assets for pension plans with accumulated benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.

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- Definition

If aggregate disclosures are presented, the aggregate projected benefit obligation for pension plans with accumulated benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.

+ References+ Details