Loans (TDR Modifications) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Number of Loans Modified as a Troubled Debt Restructuring	23	0
Pre-Modification Recorded Investment	$ 15,458	$ 0
Post-Modification Recorded Investment	$ 15,458	$ 0
Commercial Real Estate [Member]
Number of Loans Modified as a Troubled Debt Restructuring	3	0
Pre-Modification Recorded Investment	$ 1,798	$ 0
Post-Modification Recorded Investment	$ 1,798	$ 0
Commercial & Industrial [Member]
Number of Loans Modified as a Troubled Debt Restructuring	5	0
Pre-Modification Recorded Investment	$ 6,844	$ 0
Post-Modification Recorded Investment	$ 6,844	$ 0
Total Commercial [Member]
Number of Loans Modified as a Troubled Debt Restructuring	8	0
Pre-Modification Recorded Investment	$ 8,642	$ 0
Post-Modification Recorded Investment	$ 8,642	$ 0
Residential Real Estate [Member]
Number of Loans Modified as a Troubled Debt Restructuring	11	0
Pre-Modification Recorded Investment	$ 5,943	$ 0
Post-Modification Recorded Investment	$ 5,943	$ 0
Home Equity [Member]
Number of Loans Modified as a Troubled Debt Restructuring	4	0
Pre-Modification Recorded Investment	$ 873	$ 0
Post-Modification Recorded Investment	$ 873	$ 0
Other Consumer [Member]
Number of Loans Modified as a Troubled Debt Restructuring	0	0
Pre-Modification Recorded Investment	$ 0	$ 0
Post-Modification Recorded Investment	$ 0	$ 0
Total Consumer [Member]
Number of Loans Modified as a Troubled Debt Restructuring	4	0
Pre-Modification Recorded Investment	$ 873	$ 0
Post-Modification Recorded Investment	$ 873	$ 0

Number of financing receivables that have been modified by troubled debt restructurings.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, before troubled debt restructuring, of financing receivable to be modified.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=pre_CommercialOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=pre_HomeequityDomain
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=pre_OtherconsumerDomain
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: