v2.4.0.8

Commitments and Contingencies (Details Textual) (USD $) In Millions, unless otherwise specified | Jun. 30, 2013
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Commitments and Contingencies (Textual) [Abstract] |
Commitments Total | $ 180.0
Commitments due 2013 | 76.4
Commitments due 2014 and 2015 | 76.7
Commitments due 2016 and 2017 | 17.6
Commitments due thereafter | $ 9.3

X
- Definition Commitments Total + References No definition available. + Details
Name: | pra_Commitments
Namespace Prefix: | pra_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | pra_CommitmentsAndContingenciesTextualAbstract
Namespace Prefix: | pra_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Commitments due in next twelve months + References No definition available. + Details
Name: | pra_CommitmentsDueInCurrentFiscalYear
Namespace Prefix: | pra_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Commitments due in second to third year + References No definition available. + Details
Name: | pra_CommitmentsDueInFiscalYear2AndFiscalYear3
Namespace Prefix: | pra_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Commitments due in fourth to fifth year + References No definition available. + Details
Name: | pra_CommitmentsDueInFiscalYear4AndFiscalYear5
Namespace Prefix: | pra_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Commitments Due In Fiscal Year 6 And Thereafter + References No definition available. + Details
Name: | pra_CommitmentsDueInFiscalYear6AndThereafter
Namespace Prefix: | pra_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant