Investments - AFS Securities with Cost Basis in Excess of Fair Value - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Investments Debt And Equity Securities [Abstract]
Available for sale securities with cost basis in excess of fair value cost basis	$ 234.8	$ 1,239.6

Available for sale securities with cost basis in excess of fair value cost basis.

No definition available.

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