Investments - Available-for-sale Securities with Cost Basis in Excess of Fair Value - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Investments Debt And Equity Securities [Abstract]
Available-for-sale fixed-maturities with cost basis in excess of fair values, cost basis	$ 2,500.0		$ 2,500.0		$ 924.4
Available-for-sale credit (gains) losses	$ 0.0	$ 0.7	$ (0.1)	$ 0.9

Available-for-sale fixed-maturities with cost basis in excess of fair values, cost basis.

No definition available.

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