Investments - Loss from Closed Currency Forward Contracts Recorded in Accumulated Other Comprehensive Income (Loss) - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net [Abstract]
Deferred loss related to closed forward contracts	$ (26.4)	$ (26.4)

Accumulated other comprehensive income loss deferred gain loss from closed contracts in net investment hedge net of tax.

No definition available.

Name:	pri_AccumulatedOtherComprehensiveIncomeLossDeferredGainLossFromClosedContractsInNetInvestmentHedgeNetOfTax
Namespace Prefix:	pri_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant