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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	115,000,000us-gaap_CommonStockSharesAuthorized		115,000,000us-gaap_CommonStockSharesAuthorized	100,000,000us-gaap_CommonStockSharesAuthorized
Common stock, par value	$ 0.001us-gaap_CommonStockParOrStatedValuePerShare		$ 0.001us-gaap_CommonStockParOrStatedValuePerShare	$ 0.001us-gaap_CommonStockParOrStatedValuePerShare
Votes entitled to, per share	1zfgn_NumberOfVotesPerCommonShare
Dividends declared	$ 0us-gaap_CommonStockDividendsPerShareDeclared
Shares of common stock reserved	16,726,699us-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	6,635us-gaap_StockRepurchasedAndRetiredDuringPeriodShares / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember	6,635us-gaap_StockRepurchasedAndRetiredDuringPeriodShares / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember

X

- 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

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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

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-Section S99

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- Definition

Face amount or stated value per share of common stock.

+ 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



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-Paragraph 30

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- Definition

The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

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-Subparagraph (SX 210.5-02.29)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



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- Definition

Number of shares that have been repurchased and retired during the period.

+ 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

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- Definition

Number Of Votes Per Common Share

+ References

No definition available.

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