Fair Value Measurements (Qualitative Information About Level 3 Assets Measured at Fair Value on a Nonrecurring Basis) (Details) - Nonrecurring [Member] - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2021	Dec. 31, 2020
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent individually analyzed loans	$ 944	$ 1,720
Loan servicing rights		7,434
Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent individually analyzed loans	$ 944	1,720
Loan servicing rights		$ 7,434
Minimum [Member] \| Collateral Dependent Individually Analyzed Loans [Member] \| Appraisals Of Collateral [Member] \| Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount for costs to sell	10.00%	0.00%
Appraisal adjustments	0.00%	0.00%
Minimum [Member] \| Loan Servicing Rights [Member] \| Valuation Technique, Discounted Cash Flow [Member] \| Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount rates		10.00%
Prepayment rates		18.00%
Maximum [Member] \| Collateral Dependent Individually Analyzed Loans [Member] \| Appraisals Of Collateral [Member] \| Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount for costs to sell	10.00%	25.00%
Appraisal adjustments	0.00%	100.00%
Maximum [Member] \| Loan Servicing Rights [Member] \| Valuation Technique, Discounted Cash Flow [Member] \| Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount rates		14.00%
Prepayment rates		42.00%
Weighted Average [Member] \| Collateral Dependent Individually Analyzed Loans [Member] \| Appraisals Of Collateral [Member] \| Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount for costs to sell	10.00%	11.00%
Appraisal adjustments	0.00%	15.00%
Weighted Average [Member] \| Loan Servicing Rights [Member] \| Valuation Technique, Discounted Cash Flow [Member] \| Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount rates		10.00%
Prepayment rates		21.00%

This represents the adjustments to appraisal values to reflect market value declines or other discounts.

No definition available.

Name:	pre_AppraisalAdjustments
Namespace Prefix:	pre_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

This represents the discount applied to appraisals of collateral for costs to sell.

+ References

No definition available.

+ Details

Name:	pre_DiscountForCostsToSell
Namespace Prefix:	pre_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953550-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Aggregate amount of servicing assets that are subsequently measured at fair value and servicing assets that are subsequently measured using the amortization method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 45
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745

+ Details

Name:	us-gaap_ServicingAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Discount rate used to estimate the fair value of servicing assets and servicing liabilities.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122596-111746

+ Details

Name:	us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Estimated rate of prepayments of principal on servicing assets and servicing liabilities.

+ References

+ Details

Name:	us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValuePrepaymentSpeed
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=pre_CollateralDependentImpairedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationTechniqueAxis=pre_AppraisalsOfCollateralMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_ServicingContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationTechniqueAxis=us-gaap_ValuationTechniqueDiscountedCashFlowMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: