Funds Held - Directly Managed (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Disclosure - Funds Held-Directly Managed [Abstract]
Funds held directly managed investments carried at fair value	$ 300,445	$ 353,995

Carrying value of those investments held in the segregated investment portfolio underlying the funds held - directly managed account that are carried at fair value, comprised of fixed maturities, short-term investments and certain other invested assets. All changes in the fair value are recorded in net realized and unrealized investment gains and losses in the Consolidated Statement of Operations.

No definition available.

Name:	pre_FundsHeldDirectlyManagedInvestmentsCarriedAtFairValue
Namespace Prefix:	pre_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant