PENSIONS AND OTHER POSTRETIREMENT BENEFITS - Summary of Activity in Level 3 Pension Assets (Details) - RIGP - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Activity in Level 3 pension assets
Fair value of plan assets at beginning of year	$ 6,743	$ 6,003
Unrealized loss	(373)	152
Fair value of plan assets at end of year	5,544	6,743
Level 3
Activity in Level 3 pension assets
Fair value of plan assets at beginning of year	2,976	3,303
Lease payments received	393	307
Unrealized loss	(656)	(327)
Transfers out of Level 3	(393)	(307)
Fair value of plan assets at end of year	$ 2,320	$ 2,976

Represents the payments received on plan assets during the period.

No definition available.

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- Definition

The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Actual Return on Plan Assets (Component of Net Periodic Postretirement Benefit Cost)
-URI http://asc.fasb.org/extlink&oid=6504192

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Actual Return on Plan Assets (Component of Net Periodic Pension Cost)
-URI http://asc.fasb.org/extlink&oid=6504226

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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- Definition

Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 30
-Section 35
-Paragraph 50
-URI http://asc.fasb.org/extlink&oid=29635418&loc=d3e12355-114930

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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- Definition

Transfers in and out of Level 3. For example, transfers due to changes in the observability of significant inputs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(iv)(02)(C)
-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)(iv)(02)(C)
-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2446-114920

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