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Summary of significant accounting policies (Details 2) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Software development costs and amortization      
Capitalized software development costs $ 4,612,457us-gaap_CapitalizedComputerSoftwareNet $ 4,904,415us-gaap_CapitalizedComputerSoftwareNet  
Amortization expense $ 1,700,000plpm_AmortizationOfCapitalizedComputerSoftware $ 1,600,000plpm_AmortizationOfCapitalizedComputerSoftware $ 1,700,000plpm_AmortizationOfCapitalizedComputerSoftware
Minimum      
Software development costs and amortization      
Estimated useful live 3 years    
Maximum      
Software development costs and amortization      
Estimated useful live 5 years