Summary of Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited interim consolidated financial statements of 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 subsidiaries, MacroGenics UK Limited and MacroGenics 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 2020 Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) on February 25, 2021.
Inventory	Inventory When the Company believes regulatory approval is probable and expects future economic benefit from the sales of a product candidate to be realized, the Company capitalizes manufacturing costs (whether internally produced or through third-party contract manufacturing organizations) as inventory. Prior to receiving its first approval from the FDA in December 2020, the Company expensed all costs incurred related to the manufacture of MARGENZA as research and development expense because of the inherent risks associated with the development of a product candidate, the uncertainty about the regulatory approval process and the lack of history for the Company of regulatory approval of drug candidates. Subsequent to FDA approval in December 2020, the Company began capitalizing its MARGENZA third-party contract manufacturing inventory costs. Inventory is composed of raw materials, work-in-process, and finished goods, which are goods that are available for sale. The Company values its inventories at the lower of cost or estimated net realizable value. The Company determines the cost of its inventories, which includes amounts related to materials and third-party contract manufacturing costs, on a first-in, first-out basis. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period, and it writes down any excess, obsolete or unsaleable inventories to their estimated realizable value in the period in which the impairment is first identified. Such write downs, should they occur, are recorded within the cost of sales in the statement of operations.
Product Revenue, Net, Reserves for Variable Consideration, Customer Discounts and Service Fees, Product Returns, Provider Chargebacks and Discounts, and Government Rebates	Product Revenue, Net The Company entered into a limited number of arrangements with specialty distributors in the United States to distribute MARGENZA. These arrangements are considered to be contracts with customers and are in the scope of Accounting Standards Codification Topic 606, Revenue from Contracts with Customers (ASC 606). The Company has written contracts with each of its customers that have a single performance obligation - to deliver products upon receipt of a customer order - and these obligations are satisfied when delivery occurs and the customer receives the product. The specialty distributors subsequently resell the Company’s product to healthcare providers. Product revenue is recorded net of applicable reserves for variable consideration, including discounts and other allowances. Shipping and handling costs for product shipments occur prior to the customer obtaining control of the goods and are recorded in cost of sales. For the three and nine months ended September 30, 2021, the shipping costs incurred were immaterial. Reserves for Variable Consideration Revenue from product sales is recorded at the net sales price, which includes estimates of variable consideration. Components of variable consideration typically include discounts, product returns, provider chargebacks and discounts and government rebates. Variable consideration is estimated following the expected value method in accordance with ASC 606 and includes such factors as current contractual and statutory requirements, specific known market events and trends, industry data, and forecasted customer buying and payment patterns. The amount of variable consideration that is included in the transaction price may be constrained and is included in the net sales price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized under the contract will not occur in a future period. Estimates of the variable consideration were not deemed constrained during the nine months ended September 30, 2021. Customer Discounts and Service Fees The Company may provide customers with discounts which are explicitly stated in the contracts. These discounts are recorded as a reduction of revenue in the period the related product revenue is recognized. In addition, these contracts may include written service arrangements whereby the Company pays fees to customers who provide services such as sales order management, data, contract administration and distribution services, at rates which the Company believes to be consistent with fair market value. The Company has determined such services received to date are not distinct from the Company’s sale of products to its customers and, therefore, these payments have been recorded as a reduction of revenue within the statement of operations. Product Returns Consistent with industry practice, the Company offers the specialty distributors product return rights pursuant to written contracts and/or Company returned goods policies. The Company estimates the amount of its product sales that may be returned by its customers and records an estimated liability and a reduction of revenue in the period the related product revenue is recognized. The Company currently estimates product returns using industry benchmarking as well as other information available, such as visibility into the inventory remaining in the distribution channel, since the Company does not have its own returns experience. The Company's estimates of product returns may be adjusted in the future based on actual returns experience, known or expected changes in the marketplace, or other factors. Provider Chargebacks and Discounts Chargebacks for fees and discounts to healthcare providers represent the estimated obligations resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices charged to customers who directly purchase the product from the Company. In such cases, customers charge the Company for the difference between what they pay for the product and the ultimate selling price to the qualified healthcare providers. The reserve for chargebacks is established in the same period that the related revenue is recognized, resulting in a reduction of product revenue. Chargeback amounts are generally determined at the time of resale to the qualified healthcare provider by customers, and the Company generally issues credits for such amounts within a few weeks of the customer’s notification to the Company of the resale. Chargebacks consist of credits the Company expects to issue for units that remain in the distribution channel at each reporting period end that the Company expects will be sold to qualified healthcare providers and chargebacks that customers have claimed, but for which the Company has not yet issued a credit. Government Rebates The Company is subject to discount and/or rebate obligations under state Medicaid programs, Medicare and contractual agreements with and statutory obligations to certain Federal and State entities. These reserves are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue. The Company’s liability for these rebates consists of invoices received for claims from prior quarters that have not been paid or for which an invoice has not yet been received, estimates of claims for the current quarter, and estimates of future claims that will be made for product that has been recognized as revenue, but which remains in the distribution channel at the end of each reporting period. Customer discounts are recorded as a reduction of accounts receivable on the consolidated balance sheets. Allowance for product returns, provider chargebacks, government and other rebates and service fees are recorded as a component of accrued expenses and other current liabilities on the consolidated balance sheets.
Cost of Product Sales	Cost of product sales Cost of product sales relates to sales of MARGENZA. These costs include material, manufacturing and shipping costs, as well as royalties payable on net sales of MARGENZA. All product costs incurred prior to FDA approval of MARGENZA in December 2020 were expensed as research and development expense. The Company expects cost of product sales to continue to be positively impacted as the Company sells through inventory that was expensed prior to FDA approval of MARGENZA. The Company is currently unable to estimate how long it will be until it begins selling product manufactured post FDA approval.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In December 2019, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (ASU 2019-12). ASU 2019-12 is part of the FASB’s overall simplification initiative and seeks to simplify the accounting for income taxes by updating certain guidance and removing certain exceptions. The updated guidance is effective for fiscal years beginning after December 15, 2020 and interim periods within those fiscal years. The adoption of this standard as of January 1, 2021 had no impact on the Company's consolidated financial statements and related disclosures. The Company has evaluated all other ASUs issued through the date the consolidated financials were issued and believes that the adoption of these ASUs will not have a material impact on the Company's consolidated financial statements
Fair Value of Financial Instruments	The Company's financial instruments consist of cash and cash equivalents, marketable securities, accounts receivable, accounts payable and accrued expenses. The carrying amount of accounts receivable, accounts payable and accrued expenses are generally considered to be representative of their respective fair values because of their short-term nature. The Company accounts for recurring and non-recurring fair value measurements in accordance with FASB Accounting Standards Codification (ASC) 820, Fair Value Measurements and Disclosures (ASC 820). ASC 820 defines fair value, establishes a fair value hierarchy for assets and liabilities measured at fair value, and requires expanded disclosures about fair value measurements. The ASC 820 hierarchy ranks the quality of reliability of inputs, or assumptions, used in the determination of fair value and requires assets and liabilities carried at fair value to be classified and disclosed in one of the following three categories: •Level 1 - Fair value is determined by using unadjusted quoted prices that are available in active markets for identical assets and liabilities. •Level 2 - Fair value is determined by using inputs other than Level 1 quoted prices that are directly or indirectly observable. Inputs can include quoted prices for similar assets and liabilities in active markets or quoted prices for identical assets and liabilities in inactive markets. Related inputs can also include those used in valuation or other pricing models, such as interest rates and yield curves that can be corroborated by observable market data. •Level 3 - Fair value is determined by inputs that are unobservable and not corroborated by market data. Use of these inputs involves significant and subjective judgments to be made by a reporting entity - e.g., determining an appropriate adjustment to a discount factor for illiquidity associated with a given security. The Company evaluates financial assets and liabilities subject to fair value measurements on a recurring basis to determine the appropriate level at which to classify them each reporting period. This determination requires the Company to make subjective judgments as to the significance of inputs used in determining fair value and where such inputs lie within the ASC 820 hierarchy.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2021

The accompanying unaudited interim consolidated financial statements of 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 subsidiaries, MacroGenics UK Limited and MacroGenics 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 2020 Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) on February 25, 2021.

Inventory

When the Company believes regulatory approval is probable and expects future economic benefit from the sales of a product candidate to be realized, the Company capitalizes manufacturing costs (whether internally produced or through third-party contract manufacturing organizations) as inventory. Prior to receiving its first approval from the FDA in December 2020, the Company expensed all costs incurred related to the manufacture of MARGENZA as research and development expense because of the inherent risks associated with the development of a product candidate, the uncertainty about the regulatory approval process and the lack of history for the Company of regulatory approval of drug candidates. Subsequent to FDA approval in December 2020, the Company began capitalizing its MARGENZA third-party contract manufacturing inventory costs.

Inventory is composed of raw materials, work-in-process, and finished goods, which are goods that are available for sale. The Company values its inventories at the lower of cost or estimated net realizable value. The Company determines the cost of its inventories, which includes amounts related to materials and third-party contract manufacturing costs, on a first-in, first-out basis. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period, and it writes down any excess, obsolete or unsaleable inventories to their estimated realizable value in the period in which the impairment is first identified. Such write downs, should they occur, are recorded within the cost of sales in the statement of operations.

Product Revenue, Net, Reserves for Variable Consideration, Customer Discounts and Service Fees, Product Returns, Provider Chargebacks and Discounts, and Government Rebates

Product Revenue, Net

The Company entered into a limited number of arrangements with specialty distributors in the United States to distribute MARGENZA. These arrangements are considered to be contracts with customers and are in the scope of Accounting Standards Codification Topic 606, Revenue from Contracts with Customers (ASC 606). The Company has written contracts with each of its customers that have a single performance obligation - to deliver products upon receipt of a customer order - and these obligations are satisfied when delivery occurs and the customer receives the product. The specialty distributors subsequently resell the Company’s product to healthcare providers. Product revenue is recorded net of applicable reserves for variable consideration, including discounts and other allowances. Shipping and handling costs for product shipments occur prior to the customer obtaining control of the goods and are recorded in cost of sales. For the three and nine months ended September 30, 2021, the shipping costs incurred were immaterial.

Reserves for Variable Consideration

Revenue from product sales is recorded at the net sales price, which includes estimates of variable consideration. Components of variable consideration typically include discounts, product returns, provider chargebacks and discounts and government rebates. Variable consideration is estimated following the expected value method in accordance with ASC 606 and includes such factors as current contractual and statutory requirements, specific known market events and trends, industry data, and forecasted customer buying and payment patterns. The amount of variable consideration that is included in the transaction price may be constrained and is included in the net sales price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized under the contract will not occur in a future period. Estimates of the variable consideration were not deemed constrained during the nine months ended September 30, 2021.

Customer Discounts and Service Fees

The Company may provide customers with discounts which are explicitly stated in the contracts. These discounts are recorded as a reduction of revenue in the period the related product revenue is recognized. In addition, these contracts may include written service arrangements whereby the Company pays fees to customers who provide services such as sales order management, data, contract administration and distribution services, at rates which the Company believes to be consistent with fair market value. The Company has determined such services received to date are not distinct from the Company’s sale of products to its customers and, therefore, these payments have been recorded as a reduction of revenue within the statement of operations.

Product Returns

Consistent with industry practice, the Company offers the specialty distributors product return rights pursuant to written contracts and/or Company returned goods policies. The Company estimates the amount of its product sales that may be returned by its customers and records an estimated liability and a reduction of revenue in the period the related product revenue is recognized. The Company currently estimates product returns using industry benchmarking as well as other information available, such as visibility into the inventory remaining in the distribution channel, since the Company does not have its own returns experience. The Company's estimates of product returns may be adjusted in the future based on actual returns experience, known or expected changes in the marketplace, or other factors.

Provider Chargebacks and Discounts

Chargebacks for fees and discounts to healthcare providers represent the estimated obligations resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices charged to customers who directly purchase the product from the Company. In such cases, customers charge the Company for the difference between what they pay for the product and the ultimate selling price to the qualified healthcare providers. The reserve for chargebacks is established in the same period that the related revenue is recognized, resulting in a reduction of product revenue. Chargeback amounts are generally determined at the time of resale to the qualified healthcare provider by customers, and the Company generally issues credits for such amounts within a few weeks of the customer’s notification to the Company of the resale. Chargebacks consist of credits the Company expects to issue for units that remain in the distribution channel at each reporting period end that the Company expects will be sold to qualified healthcare providers and chargebacks that customers have claimed, but for which the Company has not yet issued a credit.

Government Rebates

The Company is subject to discount and/or rebate obligations under state Medicaid programs, Medicare and contractual agreements with and statutory obligations to certain Federal and State entities. These reserves are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue. The Company’s liability for these rebates consists of invoices received for claims from prior quarters that have not been paid or for which an invoice has not yet been received, estimates of claims for the current quarter, and estimates of future claims that will be made for product that has been recognized as revenue, but which remains in the distribution channel at the end of each reporting period.

Customer discounts are recorded as a reduction of accounts receivable on the consolidated balance sheets. Allowance for product returns, provider chargebacks, government and other rebates and service fees are recorded as a component of accrued expenses and other current liabilities on the consolidated balance sheets.

Cost of Product Sales

Cost of product sales

Cost of product sales relates to sales of MARGENZA. These costs include material, manufacturing and shipping costs, as well as royalties payable on net sales of MARGENZA. All product costs incurred prior to FDA approval of MARGENZA in December 2020 were expensed as research and development expense. The Company expects cost of product sales to continue to be positively impacted as the Company sells through inventory that was expensed prior to FDA approval of MARGENZA. The Company is currently unable to estimate how long it will be until it begins selling product manufactured post FDA approval.

Recent Accounting Pronouncements

In December 2019, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (ASU 2019-12). ASU 2019-12 is part of the FASB’s overall simplification initiative and seeks to simplify the accounting for income taxes by updating certain guidance and removing certain exceptions. The updated guidance is effective for fiscal years beginning after December 15, 2020 and interim periods within those fiscal years. The adoption of this standard as of January 1, 2021 had no impact on the Company's consolidated financial statements and related disclosures.

The Company has evaluated all other ASUs issued through the date the consolidated financials were issued and believes that the adoption of these ASUs will not have a material impact on the Company's consolidated financial statements

Fair Value of Financial Instruments

The Company's financial instruments consist of cash and cash equivalents, marketable securities, accounts receivable, accounts payable and accrued expenses. The carrying amount of accounts receivable, accounts payable and accrued expenses are generally considered to be representative of their respective fair values because of their short-term nature. The Company accounts for recurring and non-recurring fair value measurements in accordance with FASB Accounting Standards Codification (ASC) 820, Fair Value Measurements and Disclosures (ASC 820). ASC 820 defines fair value, establishes a fair value

hierarchy for assets and liabilities measured at fair value, and requires expanded disclosures about fair value measurements. The ASC 820 hierarchy ranks the quality of reliability of inputs, or assumptions, used in the determination of fair value and requires assets and liabilities carried at fair value to be classified and disclosed in one of the following three categories:

•Level 1 - Fair value is determined by using unadjusted quoted prices that are available in active markets for identical assets and liabilities.

•Level 2 - Fair value is determined by using inputs other than Level 1 quoted prices that are directly or indirectly observable. Inputs can include quoted prices for similar assets and liabilities in active markets or quoted prices for identical assets and liabilities in inactive markets. Related inputs can also include those used in valuation or other pricing models, such as interest rates and yield curves that can be corroborated by observable market data.

•Level 3 - Fair value is determined by inputs that are unobservable and not corroborated by market data. Use of these inputs involves significant and subjective judgments to be made by a reporting entity - e.g., determining an appropriate adjustment to a discount factor for illiquidity associated with a given security.

The Company evaluates financial assets and liabilities subject to fair value measurements on a recurring basis to determine the appropriate level at which to classify them each reporting period. This determination requires the Company to make subjective judgments as to the significance of inputs used in determining fair value and where such inputs lie within the ASC 820 hierarchy.