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Related Party Transactions - Additional Information (Detail) (USD $)
0 Months Ended 12 Months Ended
Apr. 01, 2014
Dec. 31, 2014
Dec. 31, 2013
Apr. 30, 2014
Apr. 15, 2014
Related Party Transaction [Line Items]          
Fees recorded offsetting research and development expenses   $ 39,000us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty      
Proceeds from sale of equipment 30,000us-gaap_ProceedsFromSaleOfMachineryAndEquipment        
IPO [Member]          
Related Party Transaction [Line Items]          
Convertible preferred stock, shares issued upon conversion       6,826,004us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember
9,728,237us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember
Affiliated Entity [Member]          
Related Party Transaction [Line Items]          
Fees recorded offsetting research and development expenses     $ 84,000us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= us-gaap_AffiliatedEntityMember