Commitments and Contingencies	12 Months Ended
Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 17 – Commitments and Contingencies Shareholder Derivative Lawsuit On March 31, 2020, a shareholder derivative suit, captioned Johnson (Derivatively on behalf of ADTRAN) v. T. Stanton, M. Foliano, R. Shannon, and Board of Directors, case no. 5:20-cv-00447, was filed in the U.S. District Court of Northern 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 of Directors commence an investigation into the alleged wrongdoing. On December 10, 2021, after investigating the allegations in the demand with the assistance of independent counsel, the directors (Mr. Stanton abstaining) concluded that pursuing the claims asserted in the demand would not be in the Company's best interests and exercised their business judgment to refuse the demand. Since that time, the parties to the derivative litigation have stipulated that plaintiff will either dismiss his complaint or seek to amend it pursuant to a schedule to be ordered by the Court. 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 employment matters, patent rights, 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 a 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. At this time, we are unable to predict the outcome of or estimate the possible loss or range of loss, if any, associated with such legal matters. Performance Bonds Certain contracts, customers and/or 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 December 31, 2021, we had commitments related to these bonds totaling $22.9 million which expire at various dates through April 2025. As of December 31, 2020, we had commitments related to these bonds totaling $15.2 million. Although the triggering events vary from contract to contract, 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 $18.3 million as of December 31, 2021, of which $0.2 million is included in restricted cash and $18.1 million is included in long-term investments on the 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 December 31, 2021 and through the date of this report, 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 December 31, 2021.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2021

Commitments and Contingencies Disclosure [Abstract]

Note 17 – Commitments and Contingencies

Shareholder Derivative Lawsuit

On March 31, 2020, a shareholder derivative suit, captioned Johnson (Derivatively on behalf of ADTRAN) v. T. Stanton, M. Foliano, R. Shannon, and Board of Directors, case no. 5:20-cv-00447, was filed in the U.S. District Court of Northern 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 of Directors commence an investigation into the alleged wrongdoing. On December 10, 2021, after investigating the allegations in the demand with the assistance of independent counsel, the directors (Mr. Stanton abstaining) concluded that pursuing the claims asserted in the demand would not be in the Company's best interests and exercised their business judgment to refuse the demand. Since that time, the parties to the derivative litigation have stipulated that plaintiff will either dismiss his complaint or seek to amend it pursuant to a schedule to be ordered by the Court. 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 employment matters, patent rights, 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 a 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. At this time, we are unable to predict the outcome of or estimate the possible loss or range of loss, if any, associated with such legal matters.

Performance Bonds

Certain contracts, customers and/or 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 December 31, 2021, we had commitments related to these bonds totaling $22.9 million which expire at various dates through April 2025. As of December 31, 2020, we had commitments related to these bonds totaling $15.2 million. Although the triggering events vary from contract to contract, 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 $18.3 million as of December 31, 2021, of which $0.2 million is included in restricted cash and $18.1 million is included in long-term investments on the 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 December 31, 2021 and through the date of this report, 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 December 31, 2021.