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Australia Research and Development Tax Incentive - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
9 Months Ended 12 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Dec. 31, 2013
Dec. 31, 2012
Operating Loss Carryforwards [Line Items]        
Percentage of refundable tax incentive 45.00%zfgn_EffectiveIncomeTaxRateReconciliationTaxRefundsRelatedToResearchAndDevelopment   45.00%zfgn_EffectiveIncomeTaxRateReconciliationTaxRefundsRelatedToResearchAndDevelopment  
Reduction to research and development expenses $ (368)us-gaap_IncreaseDecreaseInIncomeTaxesReceivable $ 1,230us-gaap_IncreaseDecreaseInIncomeTaxesReceivable $ 1,237us-gaap_IncreaseDecreaseInIncomeTaxesReceivable $ 630us-gaap_IncreaseDecreaseInIncomeTaxesReceivable
Unrealized foreign currency exchange (gains) losses 31us-gaap_ForeignCurrencyTransactionGainLossUnrealized 169us-gaap_ForeignCurrencyTransactionGainLossUnrealized 250us-gaap_ForeignCurrencyTransactionGainLossUnrealized  
Tax incentive receivable 1,218us-gaap_IncomeTaxesReceivable   1,617us-gaap_IncomeTaxesReceivable  
Australia [Member]        
Operating Loss Carryforwards [Line Items]        
Tax incentive receivable 1,218us-gaap_IncomeTaxesReceivable
/ us-gaap_StatementGeographicalAxis
= country_AU
  1,617us-gaap_IncomeTaxesReceivable
/ us-gaap_StatementGeographicalAxis
= country_AU
630us-gaap_IncomeTaxesReceivable
/ us-gaap_StatementGeographicalAxis
= country_AU
Percentage of reduction in research and development costs 45.00%zfgn_PercentageReductionResearchAndDevelopmentCosts
/ us-gaap_StatementGeographicalAxis
= country_AU
  45.00%zfgn_PercentageReductionResearchAndDevelopmentCosts
/ us-gaap_StatementGeographicalAxis
= country_AU
 
Tax Incentive [Member]        
Operating Loss Carryforwards [Line Items]        
Unrealized foreign currency exchange (gains) losses $ 31us-gaap_ForeignCurrencyTransactionGainLossUnrealized
/ us-gaap_IncomeTaxAuthorityAxis
= zfgn_TaxIncentiveMember
$ 169us-gaap_ForeignCurrencyTransactionGainLossUnrealized
/ us-gaap_IncomeTaxAuthorityAxis
= zfgn_TaxIncentiveMember
$ 250us-gaap_ForeignCurrencyTransactionGainLossUnrealized
/ us-gaap_IncomeTaxAuthorityAxis
= zfgn_TaxIncentiveMember