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v3.21.2

Commitments and Contingencies Purchase commitments (Details) $ in Millions | Sep. 30, 2021 USD ($)
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Subscription services commitment [Member] |
Long-term Purchase Commitment [Line Items] |
Purchase Obligation | $ 5.0
Computing Infrastructure Commitment |
Long-term Purchase Commitment [Line Items] |
Purchase Obligation | $ 17.7

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- 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_LongTermPurchaseCommitmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Minimum amount of purchase arrangement in which the entity has agreed to expend funds to procure goods or services from a supplier. + References No definition available. + Details
Name: | us-gaap_PurchaseObligation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=pro_SubscriptionServicesCommitmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=pro_ComputingInfrastructureCommitmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |