Fair Value Measurement (Details Textuals) (Details)	6 Months Ended
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

The notice period required for redemption of a particular LP valued at NAV.

No definition available.

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- 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

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Period Type:	instant

- 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

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Data Type:	xbrli:durationItemType
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Period Type:	duration

- 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

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

- Definition

The redemption percentage of a particular LP valued at NAV for which initial payment is limited.

+ References

No definition available.

+ Details

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Namespace Prefix:	pra_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

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Period Type:	duration