Name:	pl_AccumulatedOtherComprehensiveIncomeLossAccumulatedGainLossOnHedgingTax
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Period Type:	instant

The taxes related to the minimum pension liability included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s).

No definition available.

Name:	pl_AccumulatedOtherComprehensiveIncomeLossMinimumPensionLiabilityAdjustmentTax
Namespace Prefix:	pl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Income tax effect of the accumulated appreciation or loss in value of unsold securities at the end of an accounting period, other than those recorded in unrealized losses on investment securities with other-than-temporary impairment.

No definition available.

Name:	pl_AccumulatedOtherComprehensiveIncomeLossOtherUnrealizedNetGainsLossesOnInvestmentsTaxEffect
Namespace Prefix:	pl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Income tax effect of the accumulated other-than-temporary impairment losses of investments in securities, for which a portion of the other-than-temporary impairment loss has been recognized in earnings, and a portion recorded in other comprehensive income at the end of an accounting period.

No definition available.

Name:	pl_AccumulatedOtherComprehensiveIncomeLossUnrealizedOtherThanTemporaryImpairmentLossesTaxEffect
Namespace Prefix:	pl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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

The earnings that is allocated to common stock and participating securities to the extent that each security may share in earnings as if all of the earnings for the period had been distributed.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 65
-URI http://asc.fasb.org/extlink&oid=64863997&loc=d3e2793-109256

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60A
-URI http://asc.fasb.org/extlink&oid=64863997&loc=SL5780132-109256

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 66
-URI http://asc.fasb.org/extlink&oid=64863997&loc=d3e2814-109256

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60
-URI http://asc.fasb.org/extlink&oid=64863997&loc=d3e2740-109256

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60B
-URI http://asc.fasb.org/extlink&oid=64863997&loc=SL5780133-109256