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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

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- Definition Assets excluding separate account assets. + References No definition available. + Details
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Namespace Prefix: | pri_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

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