Commitments and Contingencies	9 Months Ended
Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	18. COMMITMENTS AND CONTINGENCIES Shareholder Derivative Lawsuit On March 31, 2020, a shareholder derivative suit, captioned Johnson (Derivatively on behalf of ADTRAN) v. Stanton, et al., Case No. 5:20-cv-00447, was filed in the U.S. District Court for the Northern District of Alabama against two of the Company’s current executive officers, one of its former executive officers, and certain current and former members of its Board of Directors. The derivative suit alleges, among other things, that the defendants made or caused the Company to make materially false and misleading statements regarding, and/or failed to disclose material adverse facts about, the Company’s business, operations and prospects, specifically relating to the Company’s internal control over financial reporting, excess and obsolete inventory reserves, financial results and demand from certain customers. The case was temporarily stayed pending an order on the defendants’ motion to dismiss in a separate securities class action case that included similar factual allegations, Burbridge v. ADTRAN, Inc., et al., Case No. 5:20-cv-00050-LCB (N.D. Ala.). The Burbridge case was dismissed on March 31, 2021, and the time to appeal the dismissal has expired, such that the dismissal is now final. Following the dismissal, the plaintiff in the shareholder derivative suit sent a demand letter dated June 29, 2021 to ADTRAN’s Board of Directors. The letter contains similar allegations to those made in the plaintiff’s filed complaint and in the now dismissed securities class action, and it demands, among other things, that the Board commence an investigation into the alleged wrongdoing. We expect that the derivative suit will remain stayed pending the Board’s response to the demand. At this time, we are unable to predict the outcome of or estimate the possible loss or range of loss, if any, associated with the derivative lawsuit or the demand letter. Other Legal Matters In addition to the litigation described above, from time to time we are subject to or otherwise involved in various lawsuits, claims, investigations and legal proceedings that arise out of or are incidental to the conduct of our business (collectively, “Legal Matters”), including those relating to patent rights, employment matters, regulatory compliance matters, stockholder claims, and contractual and other commercial disputes. Such Legal Matters, even if not meritorious, could result in the expenditure of significant financial and managerial resources. Additionally, an unfavorable outcome in any legal matter, including in a patent dispute, could require the Company to pay damages, entitle claimants to other relief, such as royalties, or could prevent the Company from selling some of its products in certain jurisdictions. While the Company cannot predict with certainty the results of the Legal Matters in which it is currently involved, the Company does not expect that the ultimate outcome of such Legal Matters will individually or in the aggregate have a material adverse effect on its business, results of operations, financial condition or cash flows. Business Combination Agreement On August 30, 2021, the Company, and ADVA Optical Networking SE, a European stock corporation incorporated under the laws of the European Union and Germany (“ADVA”), entered into a business combination agreement (the “Business Combination Agreement”), pursuant to which both companies agreed to combine their respective businesses and each become subsidiaries of a new holding company, Acorn HoldCo, Inc. (the "surviving corporation"), a Delaware corporation and currently a wholly-owned direct subsidiary of the Company. Under the terms of the Business Combination Agreement, Acorn MergeCo, Inc., a newly formed Delaware corporation and wholly-owned direct subsidiary of Acorn HoldCo (“Merger Sub”), will merge with and into ADTRAN, with ADTRAN surviving the merger (the “Merger”) as a wholly-owned direct subsidiary of Acorn HoldCo. Pursuant to the Merger, each outstanding share of common stock of the Company will be converted into the right to receive one share of common stock of Acorn HoldCo. Acorn HoldCo will also make a public exchange offer to exchange each issued and outstanding no-par value bearer share of ADVA, pursuant to which each ADVA share tendered and accepted for exchange will be exchanged for 0.8244 shares of common stock of Acorn HoldCo (the “Exchange Offer”, and together with the Merger, the “Business Combination”). Upon completion of the Business Combination, and assuming that all of the outstanding ADVA shares are exchanged in the Exchange Offer, former ADTRAN stockholders and former ADVA shareholders will own approximately 54% and 46%, respectively, of the outstanding Acorn HoldCo shares. The Business Combination Agreement was unanimously approved by the Board of Directors of the Company and by the supervisory board and management board of ADVA. The Company anticipates consummation of the Business Combination during mid-2022, subject to customary closing conditions as well as regulatory and shareholder approvals. Acorn HoldCo has entered into an irrevocable undertaking agreement (the “Irrevocable Undertaking”) with EGORA Holding GmbH and Egora Investments GmbH (collectively, the “Supporting Shareholders”) to validly accept the public exchange offer with respect to 7,000,000 shares held by them, representing 13.7% of the share capital of ADVA. The Irrevocable Undertaking includes other customary provisions, including certain restrictions on the Supporting Shareholders from disposing of the relevant shares. Additional information about the Business Combination Agreement and proposed Business Combination is set forth in the Company’s filings with the SEC, as well as in the registration statement on Form S-4 that Acorn HoldCo filed with the SEC, which has not yet become effective. Performance Bonds Certain contracts, customers and jurisdictions in which we do business require us to provide various guarantees of performance such as bid bonds, performance bonds and customs bonds. As of September 30, 2021 and December 31, 2020, we had commitments related to these bonds totaling $20.9 million and $15.2 million, respectively, which expire at various dates through August 2024. In general we would only be liable for the amount of these guarantees in the event of default under each contract, the probability of which we believe is remote. In June 2020, the Company entered into a letter of credit with a bank to guarantee performance obligations under a contract with a certain customer. The obligations under this customer contract will be performed over multiple years. We reached the maximum value of our minimum collateral requirement of $15.0 million during the three months ended March 31, 2021 as the Company reached certain milestones through the first quarter of 2021 as outlined in the customer contract. The letter of credit was secured by a pledge of a portion of the Company’s fixed-income securities, which totaled $18.4 million as of September 30, 2021, of which $0.1 million is included in restricted cash and $18.3 million is included in long-term investments on the Condensed Consolidated Balance Sheets. This pledged collateral value will fluctuate as the Company changes the mix of the pledged collateral between restricted cash and investments. Any shortfalls in the minimum collateral value are required to be restored by the Company from available cash and cash equivalents, short-term investments and/or long-term investments. The collateral under the letter of credit will be released when all obligations under the customer contract have been met. As of September 30, 2021, the Company was in compliance with all contractual requirements under the letter of credit. Investment Commitment We have committed to invest up to an aggregate of $5.0 million in a private equity fund, of which $4.9 million has been invested as of September 30, 2021.

Commitments and Contingencies

9 Months Ended

Sep. 30, 2021

Commitments And Contingencies Disclosure [Abstract]

18. COMMITMENTS AND CONTINGENCIES

Shareholder Derivative Lawsuit

On March 31, 2020, a shareholder derivative suit, captioned Johnson (Derivatively on behalf of ADTRAN) v. Stanton, et al., Case No. 5:20-cv-00447, was filed in the U.S. District Court for the Northern District of Alabama against two of the Company’s current executive officers, one of its former executive officers, and certain current and former members of its Board of Directors. The derivative suit alleges, among other things, that the defendants made or caused the Company to make materially false and misleading statements regarding, and/or failed to disclose material adverse facts about, the Company’s business, operations and prospects, specifically relating to the Company’s internal control over financial reporting, excess and obsolete inventory reserves, financial results and demand from certain customers. The case was temporarily stayed pending an order on the defendants’ motion to dismiss in a separate securities class action case that included similar factual allegations, Burbridge v. ADTRAN, Inc., et al., Case No. 5:20-cv-00050-LCB (N.D. Ala.). The Burbridge case was dismissed on March 31, 2021, and the time to appeal the dismissal has expired, such that the dismissal is now final. Following the dismissal, the plaintiff in the shareholder derivative suit sent a demand letter dated June 29, 2021 to ADTRAN’s Board of Directors. The letter contains similar allegations to those made in the plaintiff’s filed complaint and in the now dismissed securities class action, and it demands, among other things, that the Board commence an investigation into the alleged wrongdoing. We expect that the derivative suit will remain stayed pending the Board’s response to the demand. At this time, we are unable to predict the outcome of or estimate the possible loss or range of loss, if any, associated with the derivative lawsuit or the demand letter.

Other Legal Matters

In addition to the litigation described above, from time to time we are subject to or otherwise involved in various lawsuits, claims, investigations and legal proceedings that arise out of or are incidental to the conduct of our business (collectively, “Legal Matters”), including those relating to patent rights, employment matters, regulatory compliance matters, stockholder claims, and contractual and other commercial disputes. Such Legal Matters, even if not meritorious, could result in the expenditure of significant financial and managerial resources. Additionally, an unfavorable outcome in any legal matter, including in a patent dispute, could require the Company to pay damages, entitle claimants to other relief, such as royalties, or could prevent the Company from selling some of its products in certain jurisdictions. While the Company cannot predict with certainty the results of the Legal Matters in which it is currently involved, the Company does not expect that the ultimate outcome of such Legal Matters will individually or in the aggregate have a material adverse effect on its business, results of operations, financial condition or cash flows.

Business Combination Agreement

On August 30, 2021, the Company, and ADVA Optical Networking SE, a European stock corporation incorporated under the laws of the European Union and Germany (“ADVA”), entered into a business combination agreement (the “Business Combination Agreement”), pursuant to which both companies agreed to combine their respective businesses and each become subsidiaries of a new holding company, Acorn HoldCo, Inc. (the "surviving corporation"), a Delaware corporation and currently a wholly-owned direct subsidiary of the Company.

Under the terms of the Business Combination Agreement, Acorn MergeCo, Inc., a newly formed Delaware corporation and wholly-owned direct subsidiary of Acorn HoldCo (“Merger Sub”), will merge with and into ADTRAN, with ADTRAN surviving the merger (the “Merger”) as a wholly-owned direct subsidiary of Acorn HoldCo. Pursuant to the Merger, each outstanding share of common stock of the Company will be converted into the right to receive one share of common stock of Acorn HoldCo. Acorn HoldCo will also make a public exchange offer to exchange each issued and outstanding no-par value bearer share of ADVA, pursuant to which each ADVA share tendered and accepted for exchange will be exchanged for 0.8244 shares of common stock of Acorn HoldCo (the “Exchange Offer”, and together with the Merger, the “Business Combination”). Upon completion of the Business Combination, and assuming that all of the outstanding ADVA shares are exchanged in the Exchange Offer, former ADTRAN stockholders and former ADVA shareholders will own approximately 54% and 46%, respectively, of the outstanding Acorn HoldCo shares.

The Business Combination Agreement was unanimously approved by the Board of Directors of the Company and by the supervisory board and management board of ADVA. The Company anticipates consummation of the Business Combination during mid-2022, subject to customary closing conditions as well as regulatory and shareholder approvals.

Acorn HoldCo has entered into an irrevocable undertaking agreement (the “Irrevocable Undertaking”) with EGORA Holding GmbH and Egora Investments GmbH (collectively, the “Supporting Shareholders”) to validly accept the public exchange offer with respect to 7,000,000 shares held by them, representing 13.7% of the share capital of ADVA. The Irrevocable Undertaking includes other customary provisions, including certain restrictions on the Supporting Shareholders from disposing of the relevant shares.

Additional information about the Business Combination Agreement and proposed Business Combination is set forth in the Company’s filings with the SEC, as well as in the registration statement on Form S-4 that Acorn HoldCo filed with the SEC, which has not yet become effective.

Performance Bonds

Certain contracts, customers and jurisdictions in which we do business require us to provide various guarantees of performance such as bid bonds, performance bonds and customs bonds. As of September 30, 2021 and December 31, 2020, we had commitments related to these bonds totaling $20.9 million and $15.2 million, respectively, which expire at various dates through August 2024. In general we would only be liable for the amount of these guarantees in the event of default under each contract, the probability of which we believe is remote.

In June 2020, the Company entered into a letter of credit with a bank to guarantee performance obligations under a contract with a certain customer. The obligations under this customer contract will be performed over multiple years. We reached the maximum value of our minimum collateral requirement of $15.0 million during the three months ended March 31, 2021 as the Company reached certain milestones through the first quarter of 2021 as outlined in the customer contract. The letter of credit was secured by a pledge of a portion of the Company’s fixed-income securities, which totaled $18.4 million as of September 30, 2021, of which $0.1 million is included in restricted cash and $18.3 million is included in long-term investments on the Condensed Consolidated Balance Sheets. This pledged collateral value will fluctuate as the Company changes the mix of the pledged collateral between restricted cash and investments. Any shortfalls in the minimum collateral value are required to be restored by the Company from available cash and cash equivalents, short-term investments and/or long-term investments. The collateral under the letter of credit will be released when all obligations under the

customer contract have been met. As of September 30, 2021, the Company was in compliance with all contractual requirements under the letter of credit.

Investment Commitment

We have committed to invest up to an aggregate of $5.0 million in a private equity fund, of which $4.9 million has been invested as of September 30, 2021.