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Organization and Nature of Operations - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
 12 Months Ended 0 Months Ended
Dec. 31, 2013
Oct. 16, 2013
IPO [Member]
Organization And Nature Of Business [Line Items]    
MacroGenics incorporated date Aug. 14, 2000  
Initial public offering number of share sold   5,750,000
Initial public offering price per share   $ 16.00
Proceeds from initial public offering before offering expenses   $ 85.6