Description of Business and Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation The accompanying unaudited condensed consolidated financial statements include the accounts of Mandiant, Inc. and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”), and following the requirements of the Securities and Exchange Commission (“SEC”), for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP can be condensed or omitted. These unaudited condensed consolidated financial statements have been prepared on the same basis as our annual consolidated financial statements and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, that are necessary for a fair statement of our financial information. The results of operations for the three and six months ended June 30, 2022 are not necessarily indicative of the results to be expected for the year ending December 31, 2022 or for any other interim period or for any other future year. The balance sheet as of December 31, 2021 has been derived from audited consolidated financial statements at that date but does not include all information required by U.S. GAAP for annual consolidated financial statements. The accompanying unaudited condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements and the related notes thereto for the year ended December 31, 2021 included in our Annual Report on Form 10-K for the year ended December 31, 2021.
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Such management estimates include, but are not limited to, determining the nature and timing of satisfaction of performance obligations, useful life of our security appliances that are dependent on intelligence and assessing the material rights associated with it, determining the standalone selling price of performance obligations, subscriptions and services, commissions expense including the period of benefit of customer acquisition cost, bonus expense, future taxable income, contract manufacturer liabilities, litigation and settlement costs and other loss contingencies, fair value of our equity awards, achievement of targets for performance stock units, fair value of the liability and equity components of the Convertible Senior Notes (as defined in Note 10), results of operations of the Company’s discontinued operations, and the purchase price allocation of acquired businesses. We base our estimates on historical experience and on assumptions that we believe are reasonable. Changes in facts or circumstances may cause us to change our assumptions and estimates in future periods, and it is possible that actual results could differ from current or revised future estimates.
Discontinued Operations	Discontinued Operations If the disposal of the component of an entity (or group of components) represents a strategic shift that has (or will have) a major effect on an entity’s operations and financial results, it meets the criteria for discontinued operations. The results of discontinued operations, as well as any gain or loss on the disposal transaction, are presented separately, net of tax, from the results of continuing operations for all historical periods presented. The revenue and expenses included in the results of discontinued operations are the revenue and direct operating expenses incurred by the discontinued component that may be reasonably segregated from the revenue and costs of the ongoing operations of the Company. The operating results from discontinued operations have been included in our condensed consolidated financial statements. The condensed consolidated statement of cash flows presents cash flows from continuing operations along with cash flows from discontinued operations within each cash flow statement category.
Recently Adopted Accounting Pronouncements and Recent Accounting Pronouncements Not Yet Adopted	Recently Adopted Accounting Pronouncements In August 2020, the FASB issued Accounting Standards Update (“ASU”) 2020-06, Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (ASU 2020-06). This standard simplifies the accounting for certain financial instruments with characteristics of liabilities and equity, including convertible instruments and contracts in an entity’s own equity. Among other changes, ASU 2020-06 removes from U.S. GAAP the liability and equity separation model for convertible instruments with a cash conversion feature, and as a result, after adoption, entities will no longer separately present in equity an embedded conversion feature for such debt. Similarly, the embedded conversion feature will no longer be amortized into income as interest expense over the life of the instrument. Instead, entities will account for a convertible debt instrument wholly as debt unless (1) a convertible instrument contains features that require bifurcation as a derivative under Accounting Standards Codification (“ASC”) Topic 815, Derivatives and Hedging, or (2) a convertible debt instrument was issued at a substantial premium. Among other potential impacts, this change is expected to reduce reported interest expense, increase reported net income, and result in a reclassification of certain conversion feature balance sheet amounts from stockholders’ equity to liabilities as it relates to the Convertible Senior Notes. Additionally, ASU 2020-06 requires the application of the if-converted method to calculate the impact of convertible instruments on diluted earnings per share (EPS) and includes the effect of share settlement for instruments that may be settled in cash or shares, except for certain liability-classified share-based payment awards. The Company adopted ASU 2020-06 on January 1, 2022, using the modified retrospective basis. Adoption resulted in a $202.3 million decrease to the opening balance of accumulated deficit, $271.5 million decrease to the opening balance of additional paid-in capital, and $69.1 million increase to the opening balance of the Convertible Senior Notes, net on the condensed consolidated balance sheet. Recent Accounting Pronouncements Not Yet Adopted In October 2021, the FASB issued ASU 2021-08, Business Combinations (Topic 805): Accounting for Contract Assets and Contract Liabilities from Contracts with Customers. This standard requires an acquiring entity to apply Topic 606, Revenue from Contracts with Customers, to recognize and measure contract assets and contract liabilities in a business combination in a manner consistent with how the acquiree recognized and measured them in its preacquisition financial statements. ASU 2021-08 is effective for fiscal years beginning after December 15, 2022, including interim periods within those fiscal years. Early adoption of the amendments is permitted, including adoption in an interim period. We are currently evaluating the timing and overall impact of this standard on our condensed consolidated financial statements.
Fair Value Measurements	The accounting guidance for fair value measurements provides a framework for measuring fair value on either a recurring or nonrecurring basis, whereby the inputs used in our valuation techniques are assigned a hierarchical level. The following are the three levels of inputs to measure fair value: •Level 1: Observable inputs that reflect quoted prices (unadjusted) for identical assets or liabilities in active markets. •Level 2: Inputs that reflect quoted prices for identical assets or liabilities in less active markets; quoted prices for similar assets or liabilities in active markets; benchmark yields, reported trades, broker/dealer quotes, inputs other than quoted prices that are observable for the assets or liabilities; or inputs that are derived principally from or corroborated by observable market data by correlation or other means. •Level 3: Unobservable inputs that reflect our own assumptions incorporated in valuation techniques used to measure fair value. These assumptions are required to be consistent with market participant assumptions that are reasonably available. We consider an active market to be one in which transactions for the asset or liability occur with sufficient frequency and volume to provide pricing information on an ongoing basis, and consider an inactive market to be one in which there are infrequent or few transactions for the asset or liability, the prices are not current, or price quotations vary substantially either over time or among market makers. Where appropriate, our own or the counterparty’s non-performance risk is considered in measuring the fair values of assets.