Investments - Amortized Cost and Fair Value of AFS Fixed-maturity Securities in Default (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investments Debt And Equity Securities [Abstract]
Available-for-sale fixed-maturity securities in default, amortized cost	$ 503	$ 5
Available-for-sale fixed-maturity securities in default, fair value	$ 654	$ 125

Available for sale fixed maturity securities in default amortized cost.

No definition available.

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