Employee Benefit Plan	12 Months Ended
Dec. 31, 2018
Retirement Benefits [Abstract]
Employee Benefit Plan	Employee Benefit PlanIn 2002, the Company established the MacroGenics 401(k) Plan (the Plan) for its employees under Section 401(k) of the IRC. Under this Plan, all employees at least 21 years of age are eligible to participate in the Plan, starting on the first day of each month. Employees may contribute up to 100% of their salary, subject to government maximums.Employees are 100% vested in their contributions to the Plan. The Company's contribution to the Plan, as determined by the Board of Directors, is discretionary. The Company's contributions to the Plan totaled $1.3 million, $1.1 million and $1.0 million for the years ended December 31, 2018, 2017 and 2016, respectively.

Employee Benefit Plan

12 Months Ended

Dec. 31, 2018

Employee Benefit PlanIn 2002, the Company established the MacroGenics 401(k) Plan (the Plan) for its employees under Section 401(k) of the IRC. Under this Plan, all employees at least 21 years of age are eligible to participate in the Plan, starting on the first day of each month. Employees may contribute up to 100% of their salary, subject to government maximums.Employees are 100% vested in their contributions to the Plan. The Company's contribution to the Plan, as determined by the Board of Directors, is discretionary. The Company's contributions to the Plan totaled $1.3 million, $1.1 million and $1.0 million for the years ended December 31, 2018, 2017 and 2016, respectively.