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Quarterly Results Narrative (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
--- | ---
Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014
Quarterly Financial Information Disclosure [Abstract] |  |  |
Adjustment to gross profit | $ 1pro_Adjustmenttogrossprofit | $ 1pro_Adjustmenttogrossprofit | $ 1pro_Adjustmenttogrossprofit

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- Definition Adjustment to gross profit + References No definition available. + Details
Name: | pro_Adjustmenttogrossprofit
Namespace Prefix: | pro_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_QuarterlyFinancialInformationDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration