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Organization and Nature of Operations - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified | 9 Months Ended | 1 Months Ended |
--- | --- | --- | ---
Sep. 30, 2013 Segment | Oct. 31, 2013 Subsequent Event [Member] IPO [Member] | Oct. 16, 2013 Subsequent Event [Member] IPO [Member]
Organization And Nature Of Business [Line Items] |  |  |
MacroGenics incorporated date | Aug. 14, 2000 |  |
Number of operating segments | 1 |  |
Initial public offering number of share sold |  | 5,750,000 |
Initial public offering price per share |  |  | $ 16
Proceeds from initial public offering before offering expenses |  | $ 85.6 |

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