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Summary of Significant Accounting Policies Significant Accounting Policies (Details) (USD $)
 1 Months Ended 12 Months Ended
Feb. 28, 2014
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Summary of Significant Accounting Policies [Line Items]        
Inducement grants - Feb 2014 308,250pro_InducementgrantsFeb2014      
Tangible Asset Impairment Charges   $ 4,040,000us-gaap_TangibleAssetImpairmentCharges $ 0us-gaap_TangibleAssetImpairmentCharges $ 0us-gaap_TangibleAssetImpairmentCharges
percentage of total revenue   100.00%pro_PercentageOfTotalRevenue 100.00%pro_PercentageOfTotalRevenue 100.00%pro_PercentageOfTotalRevenue
Total shareholder return period, in years, for vesting of MSUs   three    
Shares issuable upon vesting of MSUs, maximum   200.00%pro_SharesIssuableUponVestingOfMsusMaximum    
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized   $ 45,600,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized    
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition   2 years 5 months 0 days    
Term License [Member]        
Summary of Significant Accounting Policies [Line Items]        
percentage of total revenue   2.90%pro_PercentageOfTotalRevenue
/ pro_RevenueComponentAxis
= pro_TermLicenseMember		 3.60%pro_PercentageOfTotalRevenue
/ pro_RevenueComponentAxis
= pro_TermLicenseMember		 4.80%pro_PercentageOfTotalRevenue
/ pro_RevenueComponentAxis
= pro_TermLicenseMember