Fair Value Measurement (Investments in LLCs and Limited Partnerships) (Details) $ in Thousands	3 Months Ended
Mar. 31, 2024 USD ($) fund	Dec. 31, 2023 USD ($)
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	$ 246,143	$ 245,455
Private debt funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Number of limited partners in investment \| fund	2
Number of limited partners to allow redemption by special consent \| fund	1
Private debt funds \| Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Liquidating investments remaining period	3 years
Private debt funds \| Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Liquidating investments remaining period	8 years
Private debt funds \| Investment in unconsolidated subsidiaries
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Contractual Commitments	$ 4,565
Fair Value	$ 16,768	19,886
Long/short equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Number of limited partners in investment \| fund	1
Payment period for redemption of LP valued at NAV	30 days
Long/short equity funds \| Investment in unconsolidated subsidiaries
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Contractual Commitments	$ 0
Fair Value	$ 4,243	4,497
Non-public equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Number of limited partners in investment \| fund	2
Liquidating investments remaining period	10 years
Non-public equity funds \| Investment in unconsolidated subsidiaries
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Contractual Commitments	$ 38,970
Fair Value	$ 115,421	111,251
Credit funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Number of limited partners in investment \| fund	2
Number of limited partners to allow redemption by special consent \| fund	1
Investment redemption notice period	180 days
Number of limited partners to allow redemption by special consent of partner \| fund	2
Credit funds \| Investment in unconsolidated subsidiaries
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Contractual Commitments	$ 31,552
Fair Value	$ 56,595	55,740
Strategy focused funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Number of limited partners not permitted for redemption \| fund	3
Number of limited partners, redemption allowed with prior notice \| fund	2
Strategy focused funds \| Investment in unconsolidated subsidiaries
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Contractual Commitments	$ 50,427
Fair Value	$ 53,116	$ 54,081

Fair Value, Investments, Entities that Calculate Net Asset Value, Investment Redemption, Notice Period, One Fund

No definition available.

Name:	pra_FairValueInvestmentsEntitiesThatCalculateNetAssetValueInvestmentRedemptionNoticePeriodOneFund
Namespace Prefix:	pra_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of Limited Partners Not Permitted for Redemption

+ References

No definition available.

+ Details

Name:	pra_NumberOfLimitedPartnersNotPermittedForRedemption
Namespace Prefix:	pra_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of Limited Partners, Redemption Allowed with Prior Notice

+ References

No definition available.

+ Details

Name:	pra_NumberOfLimitedPartnersRedemptionAllowedWithPriorNotice
Namespace Prefix:	pra_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of Limited Partners to Allow Redemption by Special Consent of Partner

+ References

No definition available.

+ Details

Name:	pra_NumberOfLimitedPartnersToAllowRedemptionBySpecialConsentOfPartner
Namespace Prefix:	pra_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of Limited Partners In Investment

+ References

No definition available.

+ Details

Name:	pra_NumberofLimitedPartnersInInvestment
Namespace Prefix:	pra_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of Limited Partners to Allow Redemption by Special Consent

+ References

No definition available.

+ Details

Name:	pra_NumberofLimitedPartnerstoAllowRedemptionbySpecialConsent
Namespace Prefix:	pra_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of days required for payment upon redemption of a particular LP that is valued at NAV.

+ References

No definition available.

+ Details

Name:	pra_PaymentPeriodForRedemptionOfLPValuedAtNAV
Namespace Prefix:	pra_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 54B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482134/820-10-35-54B

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-6A

+ Details

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

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

- Definition

Remaining period of expected liquidation by investee of underlying asset of investment measured at net asset value per share or unit. In 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-6A

+ Details

Name:	us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of unfunded commitments for which the entity is obligated, to those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-6A

+ Details

Name:	us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareUnfundedCommittments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_InvestmentTypeAxis=pra_PrivateDebtFundsMember
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:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=pra_InvestmentsInUnconsolidatedSubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=pra_LongshortEquityFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_PrivateEquityFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=pra_StructuredCreditFundMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=pra_StrategyFocusedFundMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: