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Commitments and Contingencies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Commitment And Contingencies [Line Items]      
Operating lease expiration year 2023    
Allowance used and reimbursed     $ 8.4us-gaap_PaymentsForProceedsFromTenantAllowance
Rent expense under operating leases 12.5us-gaap_OperatingLeasesRentExpenseNet 11.7us-gaap_OperatingLeasesRentExpenseNet 14.1us-gaap_OperatingLeasesRentExpenseNet
Total Landlord Tenant Allowance      
Commitment And Contingencies [Line Items]      
Allowance used and reimbursed     $ 9.4us-gaap_PaymentsForProceedsFromTenantAllowance
/ us-gaap_LeaseArrangementTypeAxis
= pega_TotalAllowanceMember