v2.4.0.8

Fair Value Measurement (Details Textuals) (Details) | 6 Months Ended
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Jun. 30, 2013
Long equity fund [Member] |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |
Notice period required for redemption of LP valued at NAV | 15 days
Long/Short Equity Funds [Member] |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |
Redemption Percentage of LP at NAV for which initial payment is limited | 90.00%
Payment percentage for redemption of LP at NAV for which initial payment is limited | 90.00%
Minimum [Member] | Secured debt fund [Member] |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |
Period for return of income and capital of LP valued at NAV | 7 years
Minimum [Member] | Non-public equity funds [Member] |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |
Period for return of income and capital of LP valued at NAV | 4 years
Maximum [Member] | Secured debt fund [Member] |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |
Period for return of income and capital of LP valued at NAV | 9 years
Maximum [Member] | Long equity fund [Member] |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |
Payment period for redemption of LP valued at NAV | 10 days
Maximum [Member] | Long/Short Equity Funds [Member] |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |
Notice period required for redemption of LP valued at NAV | 45 days
Payment period for redemption of LP valued at NAV | 30 days
Maximum [Member] | Non-public equity funds [Member] |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |
Period for return of income and capital of LP valued at NAV | 7 years

X
- Definition The notice period required for redemption of a particular LP valued at NAV. + References No definition available. + Details
Name: | pra_NoticePeriodRequiredForRedemptionOfLpValuedAtNav
Namespace Prefix: | pra_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The payment percentage for redemption of a particular LP valued at NAV for which initial payment is limited by the amount being redeemed. + References No definition available. + Details
Name: | pra_PaymentPercentageForRedemptionOfLpAtNavForWhichInitialPaymentIsLimited
Namespace Prefix: | pra_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of days required for payment upon redemption of a particular LP that is valued at NAV when redemption amount is less than a given threshold amount of the requestor's capital balance. + References No definition available. + Details
Name: | pra_PaymentPeriodForRedemptionOfLpValuedAtNav
Namespace Prefix: | pra_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The period over which the investor expects the return of income and capital from a particular LP valued at NAV. + References No definition available. + Details
Name: | pra_PeriodForReturnOfIncomeAndCapitalOfLpValuedAtNav
Namespace Prefix: | pra_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The redemption percentage of a particular LP valued at NAV for which initial payment is limited. + References No definition available. + Details
Name: | pra_RedemptionPercentageOfLpAtNavForWhichInitialPaymentIsLimited
Namespace Prefix: | pra_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration