Fair Value of Investments on Deposit with Governmental Authorities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Investments [Abstract]
Fair value of investments on deposit with governmental authorities	$ 20,787	$ 19,100

Investments on Deposit with Government Authorities, Fair Value Disclosure

No definition available.

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