XML 46 R33.htm IDEA: XBRL DOCUMENT v3.7.0.1

Fair Value Measurement (Narrative) (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($) Agreement	Dec. 31, 2016 USD ($)
Credit Derivatives [Line Items]
Number of line of credit agreement | Agreement	2
Equity securities [Member]
Credit Derivatives [Line Items]
Transfer of equity securities from Level 2 to Level 1 | $	$ 35,400,000	$ 0
Standard & Poor's, BBB Rating [Member] | Corporate debt with limited observable inputs [Member]
Credit Derivatives [Line Items]
Credit rating	88.00%
NRSRO | Standard & Poor's, BBB+ Rating [Member] | Corporate debt with limited observable inputs [Member]
Credit Derivatives [Line Items]
Credit rating		84.00%

X

- Definition

Line of Credit, Number of Agreement

+ References

No definition available.

+ Details

Name:	pra_LineofCreditNumberofAgreement
Namespace Prefix:	pra_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13537-108611

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_CreditDerivativesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

+ 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 (bb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueAssetsLevel2ToLevel1TransfersAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_CreditRatingStandardPoorsAxis=us-gaap_StandardPoorsBBBRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=pra_CorporateDebtLimitedObservableInputsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	invest_CreditRatingSourceAxis=pra_NationallyRecognizedStatisticalRatingOrganizationNRSROMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_CreditRatingStandardPoorsAxis=us-gaap_StandardPoorsBBBPlusRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: