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Noncash Share-based Compensation Narrative (Details) (USD $) | 1 Months Ended | 12 Months Ended
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Feb. 28, 2014 | Feb. 29, 2012 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Share-based compensation arrangement by share-based payment, Minimum Employee Subscription rate |  |  | 1.00%pro_SharebasedcompensationarrangementbysharebasedpaymentMinimumEmployeeSubscriptionrate |  |
Inducement grants - Feb 2014 | 308,250pro_InducementgrantsFeb2014 |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized |  | 900,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized |  |  |
Total shareholder return period for vesting of MSUs |  |  | three |  |
Stock Price at Year End |  |  | $ 27.48pro_StockPriceAtYearEnd |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value |  |  | $ 4,500,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue | $ 5,200,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue | $ 600,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
Shares issuable upon vesting of MSUs, maximum |  |  | 200.00%pro_SharesIssuableUponVestingOfMsusMaximum |  |
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription Rate |  |  | 10.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate |  |
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Offering Date |  |  | 5.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPriceOfferingDate |  |
Maximum Amount Contributable by employees under ESPP- Half yearly |  |  | 5,000pro_MaximumAmountContributablebyemployeesunderESPPHalfyearly |  |
Maximum Amount Contributable By Employees Under ESPP- Annually |  |  | 10,000pro_MaximumAmountContributableByEmployeesUnderESPPAnnually |  |
Stock Issued During Period, Shares, Employee Stock Purchase Plans |  |  | 13,392us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans |  |
ESPP contributions by Employees |  |  | $ 400,000pro_ESPPcontributionsbyEmployees |  |
Market Share Units (MSUs) [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Inducement grants - Feb 2014 | 75,000pro_InducementgrantsFeb2014 / us-gaap_AwardTypeAxis = pro_MarketShareUnitsMsusMember |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number |  |  | 444,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = pro_MarketShareUnitsMsusMember | 469,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = pro_MarketShareUnitsMsusMember |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number |  |  | 444,272us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber / us-gaap_AwardTypeAxis = pro_MarketShareUnitsMsusMember | 469,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber / us-gaap_AwardTypeAxis = pro_MarketShareUnitsMsusMember |
Restricted Stock Units (RSUs) [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Inducement grants - Feb 2014 | 233,250pro_InducementgrantsFeb2014 / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number |  |  | 1,830,291us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember | 1,543,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |
Employee Stock [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized |  |  | 486,608us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockMember |  |
2007 Equity Incentive Plan [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized |  |  | 8,168,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = pro_A2007EquityIncentivePlanMember |  |
2007 Equity Incentive Plan [Member] | Market Share Units (MSUs) [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number |  |  | 369,272us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber / us-gaap_AwardTypeAxis = pro_MarketShareUnitsMsusMember / us-gaap_PlanNameAxis = pro_A2007EquityIncentivePlanMember |  |
2007 Equity Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number |  |  | 1,631,041us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember / us-gaap_PlanNameAxis = pro_A2007EquityIncentivePlanMember |  |
December 2013 Market Stock Unit Performance Award [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Total shareholder return period for vesting of MSUs |  |  | two |  |
2007 Equity Incentive Plan [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number |  |  | 3,634,758us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / pro_EquityPlanAxis = pro_A2007EquityIncentivePlanMember |  |

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- Definition ESPP contributions by Employees + References No definition available. + Details
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- Definition Inducement grants - Feb 2014 + References No definition available. + Details
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- Definition Maximum Amount Contributable By Employees Under ESPP- Annually + References No definition available. + Details
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- Definition Maximum Amount Contributable by employees under ESPP- Half yearly + References No definition available. + Details
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- Definition Share-based compensation arrangement by share-based payment, Minimum Employee Subscription rate + References No definition available. + Details
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- Definition Maximum number of shares issuable upon vesting of MSUs initially granted. + References No definition available. + Details
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- Definition Stock Price at Year End + References No definition available. + Details
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- Definition Total shareholder return period used to determine vesting of MSUs. + References No definition available. + Details
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- Definition Discount rate from fair value on offering date that participants pay for shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Number of equity instruments other than options outstanding, including both vested and non-vested instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Number of additional shares authorized for issuance under an established share-based compensation plan. + References No definition available. + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Number of options outstanding, including both vested and non-vested options. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Number of shares issued during the period as a result of an employee stock purchase plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 + Details
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