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v2.4.1.9

Credit Facility (Details) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013
Line of Credit Facility [Line Items] |  |
Debt Instrument, Face Amount | $ 50,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity |
Debt Instrument, Covenant, Minimum Amount of Cash And Cash Equivalent | 20,000,000pro_DebtInstrumentCovenantMinimumAmountofCashAndCashEquivalent |
Unamortized Debt Issuance Expense | 100,000us-gaap_UnamortizedDebtIssuanceExpense | 200,000us-gaap_UnamortizedDebtIssuanceExpense
Amortization of Financing Costs | $ 46,000us-gaap_AmortizationOfFinancingCosts | $ 50,000us-gaap_AmortizationOfFinancingCosts
LIBOR Rate [Member] |  |
Line of Credit Facility [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum | 1.50%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum / pro_InterestRateAxis = pro_LiborRateMember |
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum | 2.30%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum / pro_InterestRateAxis = pro_LiborRateMember |
Federal Funds Rate [Member] |  |
Line of Credit Facility [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum | 1.50%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum / pro_InterestRateAxis = pro_FederalFundsRateMember |
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum | 2.30%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum / pro_InterestRateAxis = pro_FederalFundsRateMember |

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- Definition Debt Instrument, Covenant, Minimum Amount of Cash And Cash Equivalent + References No definition available. + Details
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Balance Type: | debit
Period Type: | instant

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- Definition Amount of noncash expense included in interest expense to issue debt and obtain financing associated with the related debt instruments. Alternate captions include noncash interest expense. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.8) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 8 -Article 5 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 8 -Article 9 + Details
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Balance Type: | debit
Period Type: | duration

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- Definition Maximum contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Minimum contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(2)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Details
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
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- Definition The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Details
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- Details
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