v2.4.0.8

Fair Value Measurement (Details 2) (Fair Value, Inputs, Level 3 [Member], USD $) In Thousands, unless otherwise specified |  |  | 6 Months Ended |  |  | 6 Months Ended |  |  | 6 Months Ended
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Jun. 30, 2013 State and municipal bonds [Member] | Dec. 31, 2012 State and municipal bonds [Member] | Jun. 30, 2013 State and municipal bonds [Member] Market comparable securities valuation technique [Member] Minimum [Member] | Jun. 30, 2013 State and municipal bonds [Member] Market comparable securities valuation technique [Member] Maximum [Member] | Jun. 30, 2013 State and municipal bonds [Member] Market comparable securities valuation technique [Member] Weighted Average [Member] | Jun. 30, 2013 State and municipal bonds [Member] Discount cash flows valuation technique [Member] Minimum [Member] | Jun. 30, 2013 State and municipal bonds [Member] Discount cash flows valuation technique [Member] Maximum [Member] | Jun. 30, 2013 State and municipal bonds [Member] Discount cash flows valuation technique [Member] Weighted Average [Member] | Jun. 30, 2013 Corporate debt with limited observable inputs [Member] | Dec. 31, 2012 Corporate debt with limited observable inputs [Member] | Jun. 30, 2013 Corporate debt with limited observable inputs [Member] Market comparable securities valuation technique [Member] Minimum [Member] | Jun. 30, 2013 Corporate debt with limited observable inputs [Member] Market comparable securities valuation technique [Member] Maximum [Member] | Jun. 30, 2013 Corporate debt with limited observable inputs [Member] Market comparable securities valuation technique [Member] Weighted Average [Member] | Jun. 30, 2013 Corporate debt with limited observable inputs [Member] Discount cash flows valuation technique [Member] Minimum [Member] | Jun. 30, 2013 Corporate debt with limited observable inputs [Member] Discount cash flows valuation technique [Member] Maximum [Member] | Jun. 30, 2013 Corporate debt with limited observable inputs [Member] Discount cash flows valuation technique [Member] Weighted Average [Member] | Jun. 30, 2013 Asset-backed Securities, Securitized Loans and Receivables [Member] | Dec. 31, 2012 Asset-backed Securities, Securitized Loans and Receivables [Member] | Jun. 30, 2013 Asset-backed Securities, Securitized Loans and Receivables [Member] Market comparable securities valuation technique [Member] Minimum [Member] | Jun. 30, 2013 Asset-backed Securities, Securitized Loans and Receivables [Member] Market comparable securities valuation technique [Member] Maximum [Member] | Jun. 30, 2013 Asset-backed Securities, Securitized Loans and Receivables [Member] Market comparable securities valuation technique [Member] Weighted Average [Member] | Jun. 30, 2013 Asset-backed Securities, Securitized Loans and Receivables [Member] Discount cash flows valuation technique [Member] Minimum [Member] | Jun. 30, 2013 Asset-backed Securities, Securitized Loans and Receivables [Member] Discount cash flows valuation technique [Member] Maximum [Member] | Jun. 30, 2013 Asset-backed Securities, Securitized Loans and Receivables [Member] Discount cash flows valuation technique [Member] Weighted Average [Member]
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ERROR in label resolution. | $ 5,000 | $ 7,200 |  |  |  |  |  |  | $ 11,400 | $ 15,200 |  |  |  |  |  |  | $ 4,700 | $ 4,000 |  |  |  |  |  |
Comparability Adjustment |  |  | 0.00% | 10.00% | 5.00% | 0.00% | 10.00% | 5.00% |  |  | 0.00% | 5.00% | 2.50% | 0.00% | 5.00% | 2.50% |  |  | 0.00% | 5.00% | 2.50% | 0.00% | 5.00% | 2.50%

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- Definition Assets fair value inputs comparability adjustments. + References No definition available. + Details
Name: | pra_AssetsFairValueInputsComparabilityAdjustments
Namespace Prefix: | pra_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258 + Details
Name: | us-gaap_AssetsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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