MORTGAGE LOANS (Details 2) (Commercial mortgage loans, USD $) In Thousands, unless otherwise specified	6 Months Ended
Jun. 30, 2011
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 Delinquent	$ 40,759
60-89 Delinquent	10,335
Greater than 90 Delinquent	15,719
Total Delinquent	$ 66,813
Number of loans, 30-59 Delinquent	8
Number of loans, 60-89 Delinquent	3
Number of loans, Greater than 90 Delinquent	9
Number of loans, Total Delinquent	20

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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Period Type:	duration

- 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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Period Type:	duration

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

- Definition

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

+ Details

Name:	pl_FinancingReceivableNumberOfLoansEqualToGreaterThan90DaysPastDue
Namespace Prefix:	pl
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ Details

Name:	pl_FinancingReceivableNumberOfLoansPastDue
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
Namespace Prefix:	us-gaap
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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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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

+ References

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue
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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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Namespace Prefix:	us-gaap
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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