Summary of Significant Accounting Policies	9 Months Ended
Sep. 30, 2022
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	GENERAL On July 8, 2022, Acorn MergeCo, Inc. (“Merger Sub”), a Delaware corporation and wholly-owned direct subsidiary of ADTRAN Holdings, Inc. (f/k/a Acorn HoldCo, Inc.), merged with and into ADTRAN, Inc., with ADTRAN, Inc. surviving the merger as a wholly-owned direct subsidiary of ADTRAN Holdings, Inc. (the “Merger”). The Merger was consummated pursuant to the Business Combination Agreement, dated as of August 30, 2021 (the “Business Combination Agreement”), by and among ADTRAN Holdings, Inc., ADTRAN, Inc., ADVA Optical Networking SE, a company organized and existing under the laws of Germany (“ADVA”), and Merger Sub. In accordance with the Business Combination Agreement, ADTRAN Holdings, Inc. made a public offer to exchange each issued and outstanding no-par value bearer share of ADVA for 0.8244 shares of common stock, par value $0.01 per share (the “Company Common Stock”), of ADTRAN Holdings, Inc. (the “Exchange Offer” and, together with the Merger, the “Business Combination”). On July 15, 2022 (the “Exchange Offer Settlement Date”), ADTRAN Holdings, Inc. completed the Exchange Offer, in which ADTRAN Holdings, Inc. acquired 34.0 million bearer shares of ADVA, or 65.43% of ADVA’s outstanding bearer shares as of the Exchange Offer Settlement Date, in exchange for the issuance of an aggregate of 28.0 million shares of Company Common Stock. See Note 2 for additional information. On October 18, 2022, the Board of Directors of the Company and the management board of ADVA agreed on a final draft of a domination and profit and loss transfer agreement (the “DPLTA”) between the Company, as the controlling company, and ADVA, as the controlled company. The parties’ execution of the DPLTA remains subject to approval of the DPLTA by shareholders of ADVA with 75% of the votes cast in an extraordinary general meeting, which is scheduled to be held on November 30, 2022. If and when signed, effectiveness of the DPLTA is subject to the subsequent registration of the DPLTA with the commercial register (Handelsregister) of the local court (Amtsgericht) at the registered offices of ADVA, with such effectiveness to occur no earlier than January 1, 2023. The Company currently holds 33,957,538 shares of ADVA, representing 65.35% of ADVA’s outstanding shares on September 30, 2022. Unless the context otherwise indicates or requires, references in this Quarterly Report on Form 10-Q to “ADTRAN,” the “Company,” “we,” “us” and “our” refer to ADTRAN, Inc. and its consolidated subsidiaries prior to the Merger on July 8, 2022, and to ADTRAN Holdings, Inc. and its consolidated subsidiaries following the Merger. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements of ADTRAN Holdings, Inc. and its subsidiaries have been prepared pursuant to the rules and regulations of the SEC applicable to interim financial information presented in Quarterly Reports on Form 10-Q. Accordingly, certain information and notes required by generally accepted accounting principles in the United States of America (“U.S. GAAP”) for complete financial statements are not included herein. Certain prior year amounts have been reclassified to conform to the current period presentation. The December 31, 2021 Condensed Consolidated Balance Sheet is derived from audited financial statements but does not include all disclosures required by U.S. GAAP. In the opinion of management, all adjustments necessary to fairly state these interim statements have been recorded and are of a normal and recurring nature. The results of operations for an interim period are not necessarily indicative of the results for the full year. The interim financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in ADTRAN, Inc. Annual Report on Form 10-K for the year ended December 31, 2021, filed with the SEC on February 25, 2022. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expense during the reporting period. Significant estimates include allowance for credit losses on accounts receivable and contract assets, excess and obsolete inventory reserves, warranty reserves, customer rebates, determination and accrual of the deferred revenue related to performance obligations under contracts with customers, estimated costs to complete obligations associated with deferred and accrued revenues and network installations, estimated income tax provision and income tax contingencies, fair value of stock-based compensation, assessment of goodwill and other intangibles for impairment, estimated lives of intangible assets, estimated pension liability and fair value of investments. Actual amounts could differ significantly from these estimates. We assessed certain accounting matters that generally require consideration of forecasted financial information in context with the information reasonably available to us and the unknown future impacts of the SARS-CoV-2 coronavirus/COVID-19 global pandemic (or variants of the SARS-CoV-2 coronavirus), supply chain constraints, inflationary pressures, the energy crisis, currency fluctuations and political tensions as of September 30, 2022 and through the date of this report. The accounting matters assessed included, but were not limited to, the allowance for credit losses, stock-based compensation, carrying value of goodwill, intangibles and other long-lived assets, financial assets, valuation allowances for tax assets, revenue recognition and costs of revenue. Future conditions related to the magnitude and duration of the COVID-19 pandemic, as well as other factors, including supply chain constraints and inflationary pressures could result in further impacts to the Company's consolidated financial statements in future reporting periods. Recently Adopted Accounting Pronouncements In October 2021, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update ("ASU") 2021-08, Business Combinations (Topic 805) Accounting for Contract Assets and Contract Liabilities from Contracts with Customers, which would require an acquirer to recognize and measure acquired contract assets and contract liabilities in a manner consistent with how the acquiree recognized and measured them in its pre-acquisition financial statements in accordance with Topic 606, Revenue Recognition. The Company early adopted ASU 2021-08 on July 1, 2022 and the standard was applied retrospectively beginning with January 1, 2022. The effect of the adoption of this standard on the Company's Condensed Consolidated Financial Statements as of the date of this report is included in Note 2 of the Notes to Condensed Consolidated Financial Statements. Recent Accounting Pronouncements Not Yet Adopted There are currently no accounting pronouncements not yet adopted that had a material effect on the Condensed Consolidated Financial Statements.

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2022

Summary of Significant Accounting Policies

GENERAL

On July 8, 2022, Acorn MergeCo, Inc. (“Merger Sub”), a Delaware corporation and wholly-owned direct subsidiary of ADTRAN Holdings, Inc. (f/k/a Acorn HoldCo, Inc.), merged with and into ADTRAN, Inc., with ADTRAN, Inc. surviving the merger as a wholly-owned direct subsidiary of ADTRAN Holdings, Inc. (the “Merger”). The Merger was consummated pursuant to the Business Combination Agreement, dated as of August 30, 2021 (the “Business Combination Agreement”), by and among ADTRAN Holdings, Inc., ADTRAN, Inc., ADVA Optical Networking SE, a company organized and existing under the laws of Germany (“ADVA”), and Merger Sub. In accordance with the Business Combination Agreement, ADTRAN Holdings, Inc. made a public offer to exchange each issued and outstanding no-par value bearer share of ADVA for 0.8244 shares of common stock, par value $0.01 per share (the “Company Common Stock”), of ADTRAN Holdings, Inc. (the “Exchange Offer” and, together with the Merger, the “Business Combination”). On July 15, 2022 (the “Exchange Offer Settlement Date”), ADTRAN Holdings, Inc. completed the Exchange Offer, in which ADTRAN Holdings, Inc. acquired 34.0 million bearer shares of ADVA, or 65.43% of ADVA’s outstanding bearer shares as of the Exchange Offer Settlement Date, in exchange for the issuance of an aggregate of 28.0 million shares of Company Common Stock. See Note 2 for additional information.

On October 18, 2022, the Board of Directors of the Company and the management board of ADVA agreed on a final draft of a domination and profit and loss transfer agreement (the “DPLTA”) between the Company, as the controlling company, and ADVA, as the controlled company. The parties’ execution of the DPLTA remains subject to approval of the DPLTA by shareholders of ADVA with 75% of the votes cast in an extraordinary general meeting, which is scheduled to be held on November 30, 2022. If and when signed, effectiveness of the DPLTA is subject to the subsequent registration of the DPLTA with the commercial register (Handelsregister) of the local court (Amtsgericht) at the registered offices of ADVA, with such effectiveness to occur no earlier than January 1, 2023. The Company currently holds 33,957,538 shares of ADVA, representing 65.35% of ADVA’s outstanding shares on September 30, 2022. Unless the context otherwise indicates or requires, references in this Quarterly Report on Form 10-Q to “ADTRAN,” the “Company,” “we,” “us” and “our” refer to ADTRAN, Inc. and its consolidated subsidiaries prior to the Merger on July 8, 2022, and to ADTRAN Holdings, Inc. and its consolidated subsidiaries following the Merger.

1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Basis of Presentation

The accompanying unaudited Condensed Consolidated Financial Statements of ADTRAN Holdings, Inc. and its subsidiaries have been prepared pursuant to the rules and regulations of the SEC applicable to interim financial information presented in Quarterly Reports on Form 10-Q. Accordingly, certain information and notes required by generally accepted accounting principles in the United States of America (“U.S. GAAP”) for complete financial statements are not included herein. Certain prior year amounts have been reclassified to conform to the current period presentation. The December 31, 2021 Condensed Consolidated Balance Sheet is derived from audited financial statements but does not include all disclosures required by U.S. GAAP.

In the opinion of management, all adjustments necessary to fairly state these interim statements have been recorded and are of a normal and recurring nature. The results of operations for an interim period are not necessarily indicative of the results for the full year. The interim financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in ADTRAN, Inc. Annual Report on Form 10-K for the year ended December 31, 2021, filed with the SEC on February 25, 2022.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expense during the reporting period. Significant estimates include allowance for credit losses on accounts receivable and contract assets, excess and obsolete inventory reserves, warranty reserves, customer rebates, determination and accrual of the deferred revenue related to performance obligations under contracts with customers, estimated costs to complete obligations associated with deferred and accrued revenues and network installations, estimated income tax provision and income tax contingencies, fair value of stock-based compensation, assessment of goodwill and other intangibles for impairment, estimated lives of intangible assets, estimated pension liability and fair value of investments. Actual amounts could differ significantly from these estimates.

We assessed certain accounting matters that generally require consideration of forecasted financial information in context with the information reasonably available to us and the unknown future impacts of the SARS-CoV-2 coronavirus/COVID-19 global pandemic (or variants of the SARS-CoV-2 coronavirus), supply chain constraints, inflationary pressures, the energy crisis, currency fluctuations and political tensions as of September 30, 2022 and through the date of this report. The accounting matters assessed included, but were not limited to, the allowance for credit losses, stock-based compensation, carrying value of goodwill, intangibles and other long-lived assets, financial assets, valuation allowances for tax assets, revenue recognition and costs of revenue. Future conditions related to the magnitude and duration of the COVID-19 pandemic, as well as other factors, including supply chain constraints and inflationary pressures could result in further impacts to the Company's consolidated financial statements in future reporting periods.

Recently Adopted Accounting Pronouncements

In October 2021, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update ("ASU") 2021-08, Business Combinations (Topic 805) Accounting for Contract Assets and Contract Liabilities from Contracts with Customers, which would require an acquirer to recognize and measure acquired contract assets and contract liabilities in a manner consistent with how the acquiree recognized and measured them in its pre-acquisition financial statements in accordance with Topic 606, Revenue Recognition. The Company early adopted ASU 2021-08 on July 1, 2022 and the standard was applied retrospectively beginning with January 1, 2022. The effect of the adoption of this standard on the Company's Condensed Consolidated Financial Statements as of the date of this report is included in Note 2 of the Notes to Condensed Consolidated Financial Statements.

Recent Accounting Pronouncements Not Yet Adopted

There are currently no accounting pronouncements not yet adopted that had a material effect on the Condensed Consolidated Financial Statements.