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EMPLOYEE BENEFIT PLANS (Details 2) (USD $)
2 Months Ended 1 Months Ended 3 Months Ended 12 Months Ended
Mar. 31, 2015
Jan. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Defined Benefit Pension Plan        
Weighted-average assumptions used to determine benefit obligations        
Service cost - benefits earned during the period $ 2,577,000us-gaap_DefinedBenefitPlanServiceCost
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Interest cost on projected benefit obligation 2,652,000us-gaap_DefinedBenefitPlanInterestCost
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Expected return on plan assets (3,423,000)us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
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Amortization of prior service cost/(credit) (98,000)us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
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Amortization of actuarial losses 1,781,000us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
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Total net periodic benefit cost 3,489,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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Defined Benefit Pension Plan | Minimum        
Weighted-average assumptions used to determine benefit obligations        
Adjusted funding target percentage to be maintained 80.00%pl_DefinedBenefitPlanAdjustedFundingTargetAttainmentPercentageToBeMaintained
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Unfunded Excess Benefits Plan        
Weighted-average assumptions used to determine benefit obligations        
Service cost - benefits earned during the period 252,000us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= pl_UnfundedExcessBenefitPlanMember
     
Interest cost on projected benefit obligation 371,000us-gaap_DefinedBenefitPlanInterestCost
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= pl_UnfundedExcessBenefitPlanMember
     
Amortization of prior service cost/(credit) 3,000us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
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= pl_UnfundedExcessBenefitPlanMember
     
Amortization of actuarial losses 364,000us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
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= pl_UnfundedExcessBenefitPlanMember
     
Total net periodic benefit cost 990,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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= pl_UnfundedExcessBenefitPlanMember
     
Predecessor | Defined Benefit Pension Plan        
Weighted-average assumptions used to determine benefit obligations        
Discount rate (as a percent)   3.55%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
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Service cost - benefits earned during the period   974,000us-gaap_DefinedBenefitPlanServiceCost
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= us-gaap_PensionPlansDefinedBenefitMember
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2,227,000us-gaap_DefinedBenefitPlanServiceCost
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9,411,000us-gaap_DefinedBenefitPlanServiceCost
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= us-gaap_PensionPlansDefinedBenefitMember
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Interest cost on projected benefit obligation   1,002,000us-gaap_DefinedBenefitPlanInterestCost
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= us-gaap_PensionPlansDefinedBenefitMember
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2,587,000us-gaap_DefinedBenefitPlanInterestCost
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10,493,000us-gaap_DefinedBenefitPlanInterestCost
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= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
Expected return on plan assets   (1,293,000)us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
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= us-gaap_PensionPlansDefinedBenefitMember
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(3,065,000)us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
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Amortization of prior service cost/(credit)   (33,000)us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
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= us-gaap_PensionPlansDefinedBenefitMember
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(98,000)us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
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= us-gaap_PensionPlansDefinedBenefitMember
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Amortization of actuarial losses   668,000us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
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1,576,000us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
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Total net periodic benefit cost   1,318,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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= us-gaap_PensionPlansDefinedBenefitMember
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3,227,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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Contribution made by the company to its defined benefit pension plan for the plan year 2014   2,200,000pl_DefinedBenefitPlanContributionsByEmployerForPriorPlanYear
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Predecessor | Unfunded Excess Benefits Plan        
Weighted-average assumptions used to determine benefit obligations        
Discount rate (as a percent)   3.26%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
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= pl_UnfundedExcessBenefitPlanMember
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= us-gaap_PredecessorMember
   
Service cost - benefits earned during the period   95,000us-gaap_DefinedBenefitPlanServiceCost
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= pl_UnfundedExcessBenefitPlanMember
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226,000us-gaap_DefinedBenefitPlanServiceCost
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= pl_UnfundedExcessBenefitPlanMember
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954,000us-gaap_DefinedBenefitPlanServiceCost
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= pl_UnfundedExcessBenefitPlanMember
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
Interest cost on projected benefit obligation   140,000us-gaap_DefinedBenefitPlanInterestCost
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= pl_UnfundedExcessBenefitPlanMember
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406,000us-gaap_DefinedBenefitPlanInterestCost
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1,696,000us-gaap_DefinedBenefitPlanInterestCost
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Amortization of prior service cost/(credit)   1,000us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
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3,000us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
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= pl_UnfundedExcessBenefitPlanMember
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= us-gaap_PredecessorMember
 
Amortization of actuarial losses   138,000us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
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= pl_UnfundedExcessBenefitPlanMember
/ us-gaap_StatementScenarioAxis
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321,000us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
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Total net periodic benefit cost   $ 374,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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$ 956,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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Predecessor | Group life insurance plan        
Weighted-average assumptions used to determine benefit obligations        
Discount rate (as a percent)   3.79%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
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