Basis of Presentation and Summary of Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements have been prepared in accordance with GAAP. The accompanying condensed consolidated financial statements include the accounts of PubMatic, Inc. and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts of assets and liabilities reported, disclosures about contingent assets and liabilities, and reported amounts of revenue and expenses. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could materially differ from those estimates and assumptions. Due to the inherent uncertainty involved in making assumptions and estimates, events and changes in circumstances arising after September 30, 2021, including those resulting from the impacts of the COVID-19 pandemic, may result in actual outcomes that differ from those contemplated by the Company’s assumptions and estimates.
Stock-Based Compensation	Stock-Based Compensation The Company recognizes and measures compensation expense for all stock-based payment awards granted to employees, directors, and nonemployees, including stock options, restricted stock units (“RSUs”), and the employee stock purchase plan (the “ESPP”) based on the fair value of the awards on the date of grant. The fair value of stock options and shares of common stock to be issued under the ESPP is estimated using the Black Scholes option pricing model. The grant date fair value of RSUs is based on the closing market price of the Company’s Class A common stock on the date of grant. The Black Scholes option pricing model is impacted by the fair value of the Company’s common stock, as well as changes in assumptions regarding a number of highly complex and subjective variables. These variables include, but are not limited to, the expected common stock price volatility over the term of the stock options, the expected term of the stock options, risk-free interest rates, and the expected dividend yield. For additional information regarding stock-based compensation and the assumptions used for determining the fair value of stock options and ESPP awards, refer to Note 9 — “Stockholders’ Equity and Stock Option Plans.”
Net Income Per Share Attributable to Common Stockholders	Net Income Per Share Attributable to Common Stockholders Basic and diluted net income per share attributable to Class A and Class B common stock is computed in conformity with the two-class method required for participating securities. The Company considers the preferred stock as participating securities. Holders of participating securities do not have a contractual obligation to share in the Company’s losses. In accordance with the two-class method, earnings allocated to these participating securities and the related number of outstanding shares of the participating securities have been excluded from the computation of basic and diluted net income per share attributable to common stockholders. Distributed and undistributed earnings allocated to participating securities are subtracted from net income in determining net income attributable to common stockholders. Basic net income per share is computed by dividing net income attributable to common stockholders by the weighted-average number of shares of the Company’s Class A and Class B common stock outstanding. The diluted net income per share attributable to common stockholders is computed by giving effect to all dilutive securities. Diluted net income per share attributable to common stockholders is computed by dividing the resulting net income attributable to common stockholders by the weighted-average number of fully diluted common shares outstanding. During the periods when there is a net loss attributable to common stockholders, potentially dilutive common stock equivalents have been excluded from the calculation of diluted net loss per share attributable to common stockholders as their effect is anti-dilutive.
Recently Adopted Accounting Pronouncements And Not Yet Adopted	Recently Adopted Accounting Pronouncements In December 2019, the Financial Accounting Standards Board (“FASB”) issued ASU 2019-12—Simplifying the Accounting for Income Taxes (“ASU 2019-12”). ASU 2019-12 simplifies the accounting for income taxes by removing certain exceptions to general principles in Topic 740 and clarifies and amends existing guidance for clarity and consistent application. Effective on January 1, 2021, the Company adopted this standard, which did not have a material impact on the condensed consolidated financial statements and related disclosures. Recent Accounting Pronouncements Not Yet Adopted Under the Jumpstart Our Business Startups Act (the “JOBS Act”), the Company meets the definition of an emerging growth company (“EGC”) and can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company elected to use this extended transition period under the JOBS Act until such time the Company is no longer considered to be an EGC. The Company expects to cease being an EGC as of December 31, 2021, becoming a large accelerated filer. The adoption dates discussed below reflect the updated transition period for complying with accounting standards not yet adopted. In February 2016, FASB issued ASU No. 2016-02, Leases, which requires an entity to recognize right-of-use assets and lease liabilities on its balance sheet and disclose key information about leasing arrangements. The guidance offers specific accounting guidance for a lessee, lessor, and sale and leaseback transactions. Lessees and lessors are required to disclose qualitative and quantitative information about leasing arrangements to enable a user of the financial statements to assess the amount, timing, and uncertainty of cash flows arising from leases. Leases will be classified as either finance or operating, with the classification affecting the pattern of expense recognition in the income statement. The guidance is effective for the Company for fiscal year 2021 and the adoption, including the impact and required disclosures will be included in its 2021 Form 10-K. The guidance requires a modified retrospective adoption. The Company expects that most of its operating lease commitments will be recognized as operating lease liabilities and right-of-use assets upon adoption of the new guidance. In June 2016, FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). This update changes the accounting for recognizing impairments of financial assets, such that credit losses for certain types of financial instruments will be estimated based on expected losses. The update also modifies the impairment models for available-for-sale debt securities and for purchased financial assets with credit deterioration since their origination. ASU 2016-13 is effective for the Company in fiscal year 2021 and the adoption, including the impact and required disclosures will be included in its 2021 Form 10-K. The Company does not expect the adoption of this guidance to have a material impact on the Company's consolidated financial statements. In January 2017, the FASB issued ASU No. 2017-04, Intangibles—Goodwill and Other: Simplifying the Test for Goodwill Impairment (“ASU 2017-04”). ASU 2017-04 eliminates Step 2 from the goodwill impairment test which measures a goodwill impairment loss by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill. Under ASU 2017-04, an entity should perform its annual or interim goodwill impairment test by comparing the fair value of the reporting unit with its carrying amount, and should recognize an impairment loss for the amount by which the carrying amount exceeds the reporting unit’s fair value, with the loss not exceeding the total amount of goodwill allocated to that reporting unit. ASU 2017-04 will be effective for the Company in fiscal year 2021 and will be included in its 2021 Form 10-K. At adoption, this update will require a prospective approach. The Company does not expect the adoption of this guidance to have a material impact on the Company's consolidated financial statements.

Basis of Presentation and Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2021

The accompanying condensed consolidated financial statements have been prepared in accordance with GAAP. The accompanying condensed consolidated financial statements include the accounts of PubMatic, Inc. and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of the condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts of assets and liabilities reported, disclosures about contingent assets and liabilities, and reported amounts of revenue and expenses.

The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could materially differ from those estimates and assumptions. Due to the inherent uncertainty involved in making assumptions and estimates, events and changes in circumstances arising after September 30, 2021, including those resulting from the impacts of the COVID-19 pandemic, may result in actual outcomes that differ from those contemplated by the Company’s assumptions and estimates.

Stock-Based Compensation

The Company recognizes and measures compensation expense for all stock-based payment awards granted to employees, directors, and nonemployees, including stock options, restricted stock units (“RSUs”), and the employee stock purchase plan (the “ESPP”) based on the fair value of the awards on the date of grant. The fair value of stock options and shares of common stock to be issued under the ESPP is estimated using the Black Scholes option pricing model. The grant date fair value of RSUs is based on the closing market price of the Company’s Class A common stock on the date of grant. The Black Scholes option pricing model is impacted by the fair value of the Company’s common stock, as well as changes in assumptions regarding a number of highly complex and subjective variables. These variables include, but are not limited to, the expected common stock price volatility over the term of the stock options, the expected term of the stock options, risk-free interest rates, and the expected dividend yield.

For additional information regarding stock-based compensation and the assumptions used for determining the fair value of stock options and ESPP awards, refer to Note 9 — “Stockholders’ Equity and Stock Option Plans.”

Net Income Per Share Attributable to Common Stockholders

Basic and diluted net income per share attributable to Class A and Class B common stock is computed in conformity with the two-class method required for participating securities. The Company considers the preferred stock as participating securities. Holders of participating securities do not have a contractual obligation to share in the Company’s losses. In accordance with the two-class method, earnings allocated to these participating securities and the related number of outstanding shares of the participating securities have been excluded from the computation of basic and diluted net income per share attributable to common stockholders.

Distributed and undistributed earnings allocated to participating securities are subtracted from net income in determining net income attributable to common stockholders. Basic net income per share is computed by dividing net income attributable to common stockholders by the weighted-average number of shares of the Company’s Class A and Class B common stock outstanding.

The diluted net income per share attributable to common stockholders is computed by giving effect to all dilutive securities. Diluted net income per share attributable to common stockholders is computed by dividing the resulting net income attributable to common stockholders by the weighted-average number of fully diluted common

shares outstanding. During the periods when there is a net loss attributable to common stockholders, potentially dilutive common stock equivalents have been excluded from the calculation of diluted net loss per share attributable to common stockholders as their effect is anti-dilutive.

Recently Adopted Accounting Pronouncements And Not Yet Adopted

Recently Adopted Accounting Pronouncements

In December 2019, the Financial Accounting Standards Board (“FASB”) issued ASU 2019-12—Simplifying the Accounting for Income Taxes (“ASU 2019-12”). ASU 2019-12 simplifies the accounting for income taxes by removing certain exceptions to general principles in Topic 740 and clarifies and amends existing guidance for clarity and consistent application. Effective on January 1, 2021, the Company adopted this standard, which did not have a material impact on the condensed consolidated financial statements and related disclosures.

Recent Accounting Pronouncements Not Yet Adopted

Under the Jumpstart Our Business Startups Act (the “JOBS Act”), the Company meets the definition of an emerging growth company (“EGC”) and can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company elected to use this extended transition period under the JOBS Act until such time the Company is no longer considered to be an EGC. The Company expects to cease being an EGC as of December 31, 2021, becoming a large accelerated filer. The adoption dates discussed below reflect the updated transition period for complying with accounting standards not yet adopted.

In February 2016, FASB issued ASU No. 2016-02, Leases, which requires an entity to recognize right-of-use assets and lease liabilities on its balance sheet and disclose key information about leasing arrangements. The guidance offers specific accounting guidance for a lessee, lessor, and sale and leaseback transactions. Lessees and lessors are required to disclose qualitative and quantitative information about leasing arrangements to enable a user of the financial statements to assess the amount, timing, and uncertainty of cash flows arising from leases. Leases will be classified as either finance or operating, with the classification affecting the pattern of expense recognition in the income statement. The guidance is effective for the Company for fiscal year 2021 and the adoption, including the impact and required disclosures will be included in its 2021 Form 10-K. The guidance requires a modified retrospective adoption. The Company expects that most of its operating lease commitments will be recognized as operating lease liabilities and right-of-use assets upon adoption of the new guidance.

In June 2016, FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). This update changes the accounting for recognizing impairments of financial assets, such that credit losses for certain types of financial instruments will be estimated based on expected losses. The update also modifies the impairment models for available-for-sale debt securities and for purchased financial assets with credit deterioration since their origination. ASU 2016-13 is effective for the Company in fiscal year 2021 and the adoption, including the impact and required disclosures will be included in its 2021 Form 10-K. The Company does not expect the adoption of this guidance to have a material impact on the Company's consolidated financial statements.

In January 2017, the FASB issued ASU No. 2017-04, Intangibles—Goodwill and Other: Simplifying the Test for Goodwill Impairment (“ASU 2017-04”). ASU 2017-04 eliminates Step 2 from the goodwill impairment test which measures a goodwill impairment loss by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill. Under ASU 2017-04, an entity should perform its annual or interim goodwill impairment test by comparing the fair value of the reporting unit with its carrying amount, and should recognize an impairment loss for the amount by which the carrying amount exceeds the reporting unit’s fair value, with the loss not exceeding the total amount of goodwill allocated to that reporting unit. ASU 2017-04 will be effective for the Company in fiscal year 2021 and will be included in its 2021 Form 10-K. At adoption, this update will require a prospective approach. The Company does not expect the adoption of this guidance to have a material impact on the Company's consolidated financial statements.