v2.4.0.8

Commitments and Contingencies (Details Textual) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013
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