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Related Party Transactions - Additional Information (Detail) - USD ($)
12 Months Ended
Apr. 01, 2014
Dec. 31, 2014
Dec. 31, 2013
Apr. 30, 2014
Related Party Transaction [Line Items]        
Proceeds from sale of equipment $ 30,000      
IPO [Member]        
Related Party Transaction [Line Items]        
Convertible preferred stock, shares issued upon conversion       6,826,004
Affiliated Entity [Member]        
Related Party Transaction [Line Items]        
Fees recorded offsetting research and development expenses   $ 39,000 $ 84,000