MORTGAGE LOANS (Details 2) (Commercial mortgage loans, USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2011 loans years days categories
Commercial mortgage loans
Delinquent loans
Past due period at which to cease carrying accrued interest on delinquent loans (in days)	90
Past due period at which to initiate foreclosure proceedings (in days)	90
30-59 Days Delinquent	$ 40,626
60-89 Days Delinquent	6,874
Greater than 90 Days Delinquent	16,223
Total Delinquent	$ 63,723
Number of loans, 30-59 Days Delinquent	6
Number of loans, 60-89 Days Delinquent	3
Number of loans, Greater than 90 Days Delinquent	9
Number of loans, Total Delinquent	18

Represents the minimum number of days past due at which the entity's policy is to cease carrying accrued interest on loans.

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- Definition

Represents the minimum number of days past due at which the entity's policy is to initiate foreclosure proceedings.

+ Details

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- Definition

Represents the number of financing receivables that are less than 60 days past due but more than 29 days past due.

+ Details

Name:	pl_FinancingReceivableNumberOfLoans30To59DaysPastDue
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Period Type:	duration

- Definition

Represents the number of financing receivables that are less than 90 days past due but more than 59 days past due.

+ Details

Name:	pl_FinancingReceivableNumberOfLoans60To89DaysPastDue
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Period Type:	duration

- Definition

Represents the number of financing receivables that are equal to or greater than 90 days past due.

+ Details

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Namespace Prefix:	pl
Data Type:	xbrli:integerItemType
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Period Type:	duration

- Definition

Represents the number of financing receivables that are past due at the balance sheet date.

+ Details

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Namespace Prefix:	pl
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Financing receivables that are less than 60 days past due but more than 29 days past due.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7A

-URI http://asc.fasb.org/extlink&oid=6965416&loc=SL6953401-111524

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing receivables that are less than 90 days past due but more than 59 days past due.

+ References

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Financing receivables that are equal to or greater than 90 days past due.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Recorded Investment in financing receivables that are past due at the balance sheet date.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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.

+ Details

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