Issue price of senior notes.

No definition available.

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Namespace Prefix:	pri_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Balance Type:	na
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.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Latest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Earliest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Description of when the fee for available but unused credit capacity is required to be paid (for example, annually, quarterly, or monthly).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
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- Details

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Period Type:

- Details

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Balance Type:
Period Type:

- Details

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Debt - Narrative (Details) - USD ($)		1 Months Ended	12 Months Ended
Debt - Narrative (Details) - USD ($)	Dec. 19, 2017	May 31, 2017	Dec. 31, 2017	Dec. 31, 2015	Dec. 31, 2016
Debt Instrument [Line Items]
Debt instrument, face amount			$ 375,000,000		$ 375,000,000
Debt instrument, interest rate, stated percentage				4.75%
Debt instrument maturity date				Jul. 15, 2022
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 200,000,000
Debt instrument, term	5 years
Debt instrument, frequency of commitment fee payable			quarterly
Debt instrument, current borrowing capacity	$ 0
Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, face amount		$ 1,300,000,000
Maximum [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument, commitment fee percentage	0.225%
Maximum [Member] \| LIBOR Rate [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate margin	1.625%
Maximum [Member] \| Base Rate [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate margin	0.625%
Minimum [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument, commitment fee percentage	0.125%
Minimum [Member] \| LIBOR Rate [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate margin	1.125%
Minimum [Member] \| Base Rate [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate margin	0.125%
Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, face amount			$ 375,000,000
Issue price of senior notes			99.843%
Debt instrument, interest rate, stated percentage			4.75%
Debt instrument maturity date			Jul. 15, 2022
Surplus Note [Member]
Debt Instrument [Line Items]
Debt instrument, face amount			$ 737,200,000
Debt instrument, interest rate, stated percentage			4.50%
Debt instrument maturity date			Dec. 31, 2030
Debt instrument, maturity start date		Dec. 31, 2029
Debt instrument, maturity end date		Dec. 31, 2030