Name:	pl_CommercialMortgageSecuritizationsDisclosureAbstract
Namespace Prefix:	pl_
Data Type:	xbrli:stringItemType
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Represents the average size of mortgage loans on real estate held in the portfolio on the balance sheet date.

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage of the mortgage loan portfolio represented by an single tenant.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of mortgage loans on real estate due to the entity after the eleventh full fiscal year following the date of the latest balance sheet presented in the financial statements, if the loans are called at their next call dates.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of mortgage loans on real estate due to the entity in the second full fiscal year through the sixth full fiscal year following the date of the latest balance sheet presented in the financial statements, if the loans are called at their next call dates.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of mortgage loans on real estate due to the entity in the seventh full fiscal year through the eleventh full fiscal year following the date of the latest balance sheet presented in the financial statements, if the loans are called at their next call dates.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of mortgage loans on real estate due to the entity in the first full fiscal year following the date of the latest balance sheet presented in the financial statements, if the loans are called at their next call dates.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of the largest mortgage loan on real estate held in the portfolio as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Definition

Represents the loan-to-value ratio permitted on commercial mortgage loans in exchange for a participating interest in the cash flows from the underlying property.

+ References

No definition available.

+ Details

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

- Definition

Represents the average size of new mortgage loans on real estate during the reporting period.

+ References

No definition available.

+ Details

Name:	pl_MortgageLoansOnRealEstateNewMortgageLoansAverageSizeOfLoans
Namespace Prefix:	pl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the period within which the call option or interest rate reset option on the mortgage loan on real estate can be exercised.

+ References

No definition available.

+ Details

Name:	pl_MortgageLoansOnRealEstatePeriodForExerciseOfCallOptionOrInterestRateResetOption
Namespace Prefix:	pl_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents mortgage loans on real estate as a percentage of the total portfolio.

+ References

No definition available.

+ Details

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

- Definition

The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 60

-Paragraph 47

-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 SEC

-Name Regulation S-X (SX)

-Number 210

-Article 7

-Section 03

-Paragraph 1

-Subparagraph c

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(c))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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

- Definition

The stated interest rate on the mortgage loan receivable or the weighted average interest rate on a group of loans.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 948

-SubTopic 310

-Section S99

-Paragraph 1

-Subparagraph (SX 210.12-29)

-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph c

-Subparagraph Schedule IV

-Article 5

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 29

-Article 12

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 10

-Section S99

-Paragraph 6

-Subparagraph (SX 210.5-04.(c) Schedule IV)

-URI http://asc.fasb.org/extlink&oid=6882300&loc=d3e5864-122674

+ Details

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

- Details

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

- Definition

Total amount of new mortgage loans on real estate during the reporting period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 948

-SubTopic 310

-Section S99

-Paragraph 1

-Subparagraph (SX 210.12-29.6)

-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph c

-Subparagraph Schedule IV

-Article 5

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 29

-Article 12

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 10

-Section S99

-Paragraph 6

-Subparagraph (SX 210.5-04.(c) Schedule IV)

-URI http://asc.fasb.org/extlink&oid=6882300&loc=d3e5864-122674

+ Details

Name:	us-gaap_MortgageLoansOnRealEstateNewMortgageLoans
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

MORTGAGE LOANS (Details) (USD $)	12 Months Ended
MORTGAGE LOANS (Details) (USD $)	Dec. 31, 2011	Dec. 31, 2010
MORTGAGE LOANS
Mortgage loans holdings	$ 5,353,481,000	$ 4,892,829,000
Mortgage loans
Percentage of Mortgage Loans on Real Estate	100.00%
Amount of new loans funded	907,000,000
Average loan size of new loans funded	2,300,000
Average loan size of portfolio	2,600,000
Weighted-average interest rate on mortgage loans (as a percent)	6.24%
Largest single mortgage loan	38,700,000
Amount that would become due in 2012, if loans are called at their next call dates	196,600,000
Amount that would become due in 2013 through 2017, if loans are called at their next call dates	1,400,000,000
Amount that would become due in 2018 through 2022, if loans are called at their next call dates	772,900,000
Amount that would become due after 2022, if loans are called at their next call dates	272,400,000
Liberty Life
Mortgage loans
Amount of new loans funded	$ 439,000,000
Minimum
Mortgage loans
Period for exercise of call options or interest rate reset options (in years)	3
Maximum
Mortgage loans
Single tenant's exposure as a percentage of mortgage loans	2.00%
Period for exercise of call options or interest rate reset options (in years)	10
Loan-to-value ratio with participating interest (as a percent)	85.00%
All identified states
Mortgage loans
Percentage of Mortgage Loans on Real Estate	74.50%
Texas
Mortgage loans
Percentage of Mortgage Loans on Real Estate	11.90%
Georgia
Mortgage loans
Percentage of Mortgage Loans on Real Estate	9.20%
Tennessee
Mortgage loans
Percentage of Mortgage Loans on Real Estate	7.40%
Alabama
Mortgage loans
Percentage of Mortgage Loans on Real Estate	6.80%
Florida
Mortgage loans
Percentage of Mortgage Loans on Real Estate	7.00%
South Carolina
Mortgage loans
Percentage of Mortgage Loans on Real Estate	6.00%
Ohio
Mortgage loans
Percentage of Mortgage Loans on Real Estate	5.00%
Utah
Mortgage loans
Percentage of Mortgage Loans on Real Estate	4.50%
North Carolina
Mortgage loans
Percentage of Mortgage Loans on Real Estate	5.40%
Indiana
Mortgage loans
Percentage of Mortgage Loans on Real Estate	2.80%
Pennsylvania
Mortgage loans
Percentage of Mortgage Loans on Real Estate	2.60%
California
Mortgage loans
Percentage of Mortgage Loans on Real Estate	3.20%
Michigan
Mortgage loans
Percentage of Mortgage Loans on Real Estate	2.70%
Retail
Mortgage loans
Percentage of Mortgage Loans on Real Estate	65.70%
Office buildings
Mortgage loans
Percentage of Mortgage Loans on Real Estate	13.40%
Apartments
Mortgage loans
Percentage of Mortgage Loans on Real Estate	11.30%
Warehouses
Mortgage loans
Percentage of Mortgage Loans on Real Estate	7.60%
Other
Mortgage loans
Percentage of Mortgage Loans on Real Estate	2.00%