Represents the additional security provided to support the unfunded liabilities of the pension plans.

No definition available.

Name:	mlp_DefinedBenefitPlanAdditionalSecurityToSupportUnfundedLiabilities
Namespace Prefix:	mlp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the area of real estate property pledged as security.

+ References

No definition available.

+ Details

Name:	mlp_DefinedBenefitPlanAreaOfRealEstatePropertyPledgedAsSecurity
Namespace Prefix:	mlp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of pension plans that the entity was required to provide additional security for the unfunded liabilities.

+ References

No definition available.

+ Details

Name:	mlp_DefinedBenefitPlanNumberOfPensionPlansProvidedSecurity
Namespace Prefix:	mlp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the period for release of real estate property pledged as collateral.

+ References

No definition available.

+ Details

Name:	mlp_DefinedBenefitPlanPeriodForReleaseOfRealEstatePropertyPledgedAsSecurity
Namespace Prefix:	mlp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the security provided to support the unfunded liabilities of the pension plan.

+ References

No definition available.

+ Details

Name:	mlp_DefinedBenefitPlanSecurityToSupportUnfundedLiabilities
Namespace Prefix:	mlp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the number of investment and savings plans that the majority of employees are eligible to participate in.

+ References

No definition available.

+ Details

Name:	mlp_MinimumNumberOfInvestmentAndSavingsPlansMajorityOfEmployeesEligibleToParticipateIn
Namespace Prefix:	mlp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_CompensationAndRetirementDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.

+ References

No definition available.

+ Details

Name:	us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The employer's best estimate, as soon as it can be reasonably determined, of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position. Estimated contributions may be presented in the aggregate combining (1) contributions required by funding regulations or laws, (2) discretionary contributions, and (3) noncash contributions.

+ 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 (g)

-URI http://asc.fasb.org/extlink&oid=21915506&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph g

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Name:	us-gaap_DefinedBenefitPlanEstimatedFutureEmployerContributionsInNextFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of benefits expected to be paid in the five fiscal years after the fifth fiscal year following the latest fiscal year from a defined benefit plan.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of benefits expected to be paid in the next fiscal year following the latest fiscal year from a defined benefit plan.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of benefits expected to be paid in the fifth fiscal year following the latest fiscal year from a defined benefit plan.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of benefits expected to be paid in the fourth fiscal year following the latest fiscal year from a defined benefit plan.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of benefits expected to be paid in the third fiscal year following the latest fiscal year from a defined benefit plan.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of benefits expected to be paid in the second fiscal year following the latest fiscal year from a defined benefit plan.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

EMPLOYEE BENEFIT PLANS (Details 3) (USD $)	1 Months Ended		12 Months Ended
EMPLOYEE BENEFIT PLANS (Details 3) (USD $)	Nov. 30, 2012 acre	Apr. 30, 2011 acre	Dec. 31, 2012 item	Dec. 31, 2011
EMPLOYEE BENEFIT PLANS
Expected contribution to the defined benefit pension plans in the next fiscal year			$ 2,400,000
Estimated future benefit payments
2013			4,317,000
2014			4,269,000
2015			4,251,000
2016			4,330,000
2017			4,368,000
2018-2022			22,216,000
Security to support the unfunded liabilities of the Bargaining Plan			5,200,000
Area of property pledged as security (in acres)	7,000	1,400
Period for release of property pledged as collateral	5 years	5 years
Additional security to support unfunded liabilities			18,700,000
Number of pension plans			2
Minimum number of investment and savings plans majority of employees are eligible to participate in			1
Deferred compensation plan liabilities			$ 512,000	$ 697,000