Represents the average size of mortgage loans on real estate held in the portfolio on the balance sheet date.

No definition available.

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

Represents the amount of mortgage loans on real estate due to the entity after the eleventh fiscal year following the latest fiscal year, if the loans are called at their next call dates.

+ References

No definition available.

+ Details

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- Definition

Represents the amount of mortgage loans on real estate due to the entity in the next fiscal year following the latest fiscal year ended, if the loans are called at their next call dates.

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- 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

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Namespace Prefix:	pl_
Data Type:	xbrli:monetaryItemType
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- Definition

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

+ References

No definition available.

+ Details

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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:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

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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 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

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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

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-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=27047687&loc=d3e5864-122674

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- 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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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- 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

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-Name Accounting Standards Codification
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-Section S99
-Paragraph 6
-Subparagraph (SX 210.5-04.(c) Schedule IV)
-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674

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Period Type:	duration

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MORTGAGE LOANS - Loan Portfolio (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Mortgage loans
Mortgage loans holdings	$ 6,817,723	$ 6,132,125
Percentage of Mortgage Loans on Real Estate	100.00%
Amount of new loans funded	$ 1,600,000
Average loan size of new loans funded	8,800
Average loan size of portfolio	$ 4,000
Weighted-average interest rate on mortgage loans (as a percent)	4.80%
Largest single mortgage loan	$ 61,100
Amount that would become due in 2018, if loans are called at their next call dates	161,200
Amount that would become due in 2019 through 2023, if loans are called at their next call dates	858,600
Amount that would become due in 2024 through 2028, if loans are called at their next call dates	105,800
Amount that would become due after 2028, if loans are called at their next call dates	$ 2,000
Alabama
Mortgage loans
Percentage of Mortgage Loans on Real Estate	9.60%
Florida
Mortgage loans
Percentage of Mortgage Loans on Real Estate	9.40%
Texas
Mortgage loans
Percentage of Mortgage Loans on Real Estate	8.40%
Georgia
Mortgage loans
Percentage of Mortgage Loans on Real Estate	7.90%
Ohio
Mortgage loans
Percentage of Mortgage Loans on Real Estate	5.50%
Tennessee
Mortgage loans
Percentage of Mortgage Loans on Real Estate	5.30%
California
Mortgage loans
Percentage of Mortgage Loans on Real Estate	5.20%
South Carolina
Mortgage loans
Percentage of Mortgage Loans on Real Estate	3.30%
North Carolina
Mortgage loans
Percentage of Mortgage Loans on Real Estate	4.90%
Utah
Mortgage loans
Percentage of Mortgage Loans on Real Estate	4.90%
All identified states
Mortgage loans
Percentage of Mortgage Loans on Real Estate	64.40%
Retail
Mortgage loans
Percentage of Mortgage Loans on Real Estate	52.10%
Office Buildings
Mortgage loans
Percentage of Mortgage Loans on Real Estate	10.90%
Apartments
Mortgage loans
Percentage of Mortgage Loans on Real Estate	8.80%
Warehouses
Mortgage loans
Percentage of Mortgage Loans on Real Estate	10.40%
Senior housing
Mortgage loans
Percentage of Mortgage Loans on Real Estate	13.70%
Other
Mortgage loans
Percentage of Mortgage Loans on Real Estate	4.10%
Maximum
Mortgage loans
Single tenant's exposure as a percentage of mortgage loans (more than)	1.50%
Period for exercise of call options or interest rate reset options	11 years