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Stockholders' Equity (Deficit) - Summary of Number of Shares of Common Stock Reserved (Detail) | Dec. 31, 2014 | Dec. 31, 2013
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Class Of Stock [Line Items] |  |
Reserved shares of common stock | 3,689,767 us-gaap_CommonStockCapitalSharesReservedForFutureIssuance | 8,156,461 us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
Common stock options [Member] |  |
Class Of Stock [Line Items] |  |
Reserved shares of common stock | 3,561,104 us-gaap_CommonStockCapitalSharesReservedForFutureIssuance / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember | 1,201,770 us-gaap_CommonStockCapitalSharesReservedForFutureIssuance / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember
Redeemable Convertible Preferred Stock [Member] |  |
Class Of Stock [Line Items] |  |
Reserved shares of common stock |  | 6,954,691 us-gaap_CommonStockCapitalSharesReservedForFutureIssuance / us-gaap_StatementEquityComponentsAxis = us-gaap_RedeemableConvertiblePreferredStockMember
Warrants to Purchase Common Stock [Member] |  |
Class Of Stock [Line Items] |  |
Reserved shares of common stock | 128,663 us-gaap_CommonStockCapitalSharesReservedForFutureIssuance / us-gaap_StatementEquityComponentsAxis = ceru_WarrantsToPurchaseCommonStockMember |

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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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