Name:	pl_DefinedBenefitPlanFixedIncome
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Data Type:	num:percentItemType
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Period Type:	instant

The percentage of the fair value of cash and cash equivalents to the fair value of total plan assets held as of the measurement date.

No definition available.

Name:	pl_DefinedBenefitPlanOtherPlanAssetsCashAndCashEquivalents
Namespace Prefix:	pl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Target allocation percentage of investments in cash and cash equivalents to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position.

No definition available.

Name:	pl_DefinedBenefitPlanTargetAllocationPercentageOfAssetsCashAndCashEquivalents
Namespace Prefix:	pl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Target allocation percentage of fixed income to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position.

No definition available.

Name:	pl_DefinedBenefitPlanTargetAllocationPercentageOfAssetsFixedIncome
Namespace Prefix:	pl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

The target aggregate percentage of the fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of total plan assets held as of the measurement date.

No definition available.

Name:	pl_DefinedBenefitPlanWeightedAverageTargetAllocations
Namespace Prefix:	pl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

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

The percentage of the fair value of equity securities to the fair value of total plan assets held as of the measurement date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph d(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e2446-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (d)(1)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

Name:	us-gaap_DefinedBenefitPlanEquitySecurities
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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Target allocation percentage of investments in equity securities to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position.

No definition available.

Name:	us-gaap_DefinedBenefitPlanTargetAllocationPercentageOfAssetsEquitySecurities
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

The aggregate percentage of the fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of total plan assets held as of the measurement date.