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v2.4.1.9

Common Stock - Additional Information (Detail) (USD $) | 12 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Dec. 31, 2013 Vote | Sep. 30, 2013 | Sep. 30, 2014 | Dec. 31, 2012
Changes In Equity And Comprehensive Income Line Items [Line Items] |  |  |  |
Common stock, shares authorized | 115,000,000 us-gaap_CommonStockSharesAuthorized |  | 115,000,000 us-gaap_CommonStockSharesAuthorized | 100,000,000 us-gaap_CommonStockSharesAuthorized
Common stock, par value | $ 0.001 us-gaap_CommonStockParOrStatedValuePerShare |  | $ 0.001 us-gaap_CommonStockParOrStatedValuePerShare | $ 0.001 us-gaap_CommonStockParOrStatedValuePerShare
Votes entitled to, per share | 1 zfgn_NumberOfVotesPerCommonShare |  |  |
Dividends declared | $ 0 us-gaap_CommonStockDividendsPerShareDeclared |  |  |
Shares of common stock reserved | 16,726,699 us-gaap_CommonStockCapitalSharesReservedForFutureIssuance |  |  |
Common Stock [Member] |  |  |  |
Changes In Equity And Comprehensive Income Line Items [Line Items] |  |  |  |
Reacquired and retired restricted common stock | (6,635)us-gaap_StockRepurchasedAndRetiredDuringPeriodShares / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |  |
Common Stock [Member] | Restricted Stock [Member] |  |  |  |
Changes In Equity And Comprehensive Income Line Items [Line Items] |  |  |  |
Reacquired and retired restricted common stock | 6,635 us-gaap_StockRepurchasedAndRetiredDuringPeriodShares / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember | 6,635 us-gaap_StockRepurchasedAndRetiredDuringPeriodShares / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |

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- Definition Aggregate number of common shares reserved for future issuance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.29) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Aggregate dividends declared during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
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