Basis of Presentation and Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited interim consolidated financial statements of MacroGenics, Inc. (the Company) have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information. The financial statements include all adjustments (consisting only of normal recurring adjustments) that the management of the Company believes are necessary for a fair presentation of the periods presented. These interim financial results are not necessarily indicative of results expected for the full fiscal year or for any subsequent interim period. The accompanying unaudited interim consolidated financial statements include the accounts of MacroGenics, Inc. and its wholly owned subsidiary, MacroGenics UK Limited. All intercompany accounts and transactions have been eliminated in consolidation. These consolidated financial statements and related notes should be read in conjunction with the financial statements and notes thereto included in the Company's 2018 Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) on February 26, 2019.
Recently Adopted and Issued Accounting Standards	Recently Adopted Accounting Standards In February 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-02, which requires lessees to recognize a right-of-use (ROU) asset and a lease liability for all leases with terms greater than 12 months and also requires disclosures by lessees and lessors about the amount, timing and uncertainty of cash flows arising from leases. Subsequent to the issuance of ASU 2016-02, the FASB clarified the guidance through several ASUs, with the resulting guidance collectively referred to as ASC 842. The Company adopted ASC 842 effective January 1, 2019, using the optional transition method provided under ASU 2018-11, which did not require adjustments to comparative periods nor require modified disclosures in those comparative periods. The Company has elected not to recognize leases with terms of one year or less on the balance sheet. At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances. For leases where the Company is the lessee, ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent an obligation to make lease payments arising from the lease. ROU assets and lease liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes the appropriate incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term of the lease for which the rate is estimated. Certain adjustments to the ROU asset may be required for items such as initial direct costs paid or incentives received. The lease terms used to calculate the ROU asset and related lease liabilities include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense for operating leases is recognized on a straight-line basis over the lease term as an operating expense while the expense for finance leases is recognized as depreciation expense and interest expense using the accelerated interest method of recognition. The Company has lease agreements which require payments for lease and non-lease components and has elected the practical expedient not to separate non-lease components from lease components for all classes of underlying assets. As a result of the cumulative impact of adopting ASC 842, the Company recorded operating lease ROU assets of $16.4 million and operating lease liabilities of $27.7 million as of January 1, 2019, primarily related to real estate leases, based on the present value of the future lease payments on the date of adoption. The ROU asset is included in Other assets on the consolidated balance sheets. Refer to Note 4, Leases, for additional disclosures required by ASC 842. Recently Issued Accounting Standards In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808)—Clarifying the interaction between Topic 808 and Topic 606 (ASU 2018-18). The amendments provide guidance on whether certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606. It also specifically (i) addresses when the participant should be considered a customer in the context of a unit of account, (ii) adds unit-of-account guidance in ASC 808 to align with guidance in ASC 606, and (iii) precludes presenting revenue from a collaborative arrangement together with revenue recognized under ASC 606 if the collaborative arrangement participant is not a customer. The guidance will be effective for fiscal years beginning after December 15, 2019. Early adoption is permitted and should be applied retrospectively. The Company does not anticipate the adoption of this standard will have a material impact on its consolidated financial statements. The Company has evaluated all other ASUs issued through the date the consolidated financials were issued and believes that the adoption of these will not have a material impact on the Company's consolidated financial statements.