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Segment and Geographical Information - Summary of Assets and Profit or Loss by Segment (Parenthetical) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Investment and Savings Products Segment [Member]
Segment Reporting Information [Line Items]
Assets, excluding separate account assets	$ 123.6	$ 112.0

X

- Definition

Assets excluding separate account assets.

+ References

No definition available.

+ Details

Name:	pri_AssetsExcludingSeparateAccountAssets
Namespace Prefix:	pri_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- 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

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

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=us-gaap_InvestmentsSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: