SIGNIFICANT TRANSACTIONS - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2018	May 01, 2018
P L I C O
Business Combination Segment Allocation [Line Items]
Coinsurance basis percentage			100.00%
Ceded commissions for reinsurance			$ 422.9
Statutory reserves resulting from reinsurance, business acquired			$ 13,300.0
Life Business
Business Combination Segment Allocation [Line Items]
Revenue	$ 142.7	$ 142.7
Net income	7.5	7.5
Acquisition related costs	$ 5.5	$ 5.5

Reinsurance Agreement, Ceding Commissions

No definition available.

Name:	pl_ReinsuranceAgreementCedingCommissions
Namespace Prefix:	pl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Reinsurance Agreement, Coinsurance Basis Percentage

+ References

No definition available.

+ Details

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

- Definition

Reinsurance Transaction, Statutory Reserves Resulting from Reinsurance Business Acquired

+ References

No definition available.

+ Details

Name:	pl_ReinsuranceTransactionStatutoryReservesResultingfromReinsuranceBusinessAcquired
Namespace Prefix:	pl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of direct costs of the business combination including legal, accounting, and other costs incurred to consummate the business acquisition.

+ References

No definition available.

+ Details

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

- Definition

This element represents the amount of earnings or loss of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

+ Details

Name:	us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents the amount of revenue of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

+ References

+ Details

Name:	us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

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.

+ References

No definition available.

+ Details

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

- Details

Name:	dei_LegalEntityAxis=pl_PLICOMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=pl_LifeBusinessMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: