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v2.4.1.9

Convertible Promissory Notes - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified | 9 Months Ended | 12 Months Ended | 1 Months Ended |
--- | --- | --- | --- | ---
Sep. 30, 2014 | Sep. 30, 2013 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011 | Jan. 31, 2013 | Nov. 30, 2012 | Aug. 31, 2012
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Promissory notes convertible threshold percentage of preferred stock price |  |  | 90.00%zfgn_DebtInstrumentConvertibleStockPriceTriggerPercentage |  |  |  |  |
Number of redeemable convertible preferred stock issued | 0 us-gaap_TemporaryEquitySharesIssued |  | 94,483,404 us-gaap_TemporaryEquitySharesIssued | 73,991,017 us-gaap_TemporaryEquitySharesIssued |  |  |  |
Proceeds from issuance of redeemable convertible preferred stock | $ 442 us-gaap_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStock | $ 5,955 us-gaap_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStock | $ 40,799 us-gaap_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStock | $ 16,057 us-gaap_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStock | $ 10,069 us-gaap_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStock |  |  |
Series D Preferred Stock [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Promissory notes principal amount |  |  |  |  |  |  | 6,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesDPreferredStockMember |
Number of redeemable convertible preferred stock issued |  |  | 16,011,162 us-gaap_TemporaryEquitySharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesDPreferredStockMember | 11,629,248 us-gaap_TemporaryEquitySharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesDPreferredStockMember |  | 4,381,914 us-gaap_TemporaryEquitySharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesDPreferredStockMember | 6,653,988 us-gaap_TemporaryEquitySharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesDPreferredStockMember |
Proceeds from issuance of redeemable convertible preferred stock |  |  |  |  |  | 5,956 us-gaap_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStock / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesDPreferredStockMember | 9,044 us-gaap_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStock / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesDPreferredStockMember |
Outstanding principal and accrued interest amount converted |  |  |  |  |  |  | 6,086 us-gaap_DebtConversionConvertedInstrumentAmount1 / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesDPreferredStockMember |
Outstanding principal and accrued interest shares converted |  |  |  |  |  |  | 4,975,260 us-gaap_DebtConversionConvertedInstrumentSharesIssued1 / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesDPreferredStockMember |
Minimum [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Proceeds from issuance of preferred stock |  |  | 10,000 us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |  |  |
Convertible Notes Payable [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Promissory notes principal amount |  |  |  |  |  |  | $ 6,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_ShortTermDebtTypeAxis = us-gaap_ConvertibleNotesPayableMember | $ 6,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_ShortTermDebtTypeAxis = us-gaap_ConvertibleNotesPayableMember
Annual interest rate |  |  | 8.00%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_ShortTermDebtTypeAxis = us-gaap_ConvertibleNotesPayableMember |  |  |  |  |

X
- Definition The value of the financial instrument(s) that the original debt is being converted into in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586 + Details
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- Definition The number of shares issued in exchange for the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or payments in the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586 + Details
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- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400 + Details
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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Proceeds from issuance of capital stock which provides for a specific dividend that is paid to the shareholders before any dividends to common stockholders and which takes precedence over common stockholders in the event of liquidation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585 + Details
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- Definition The cash inflow from issuance of callable preferred stock which is identified as being convertible to another type of financial security at the option of the issuer or the holder. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585 + Details
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- Definition The number of securities classified as temporary equity that have been sold (or granted) to the entity's shareholders. Securities issued include securities outstanding and securities held in treasury. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer. + 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 210.5-02.27(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 28 -Subparagraph b -Article 5 + Details
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