Commitments and Contingencies	3 Months Ended
Mar. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	19. COMMITMENTS AND CONTINGENCIES Securities Class Action Lawsuit On March 31, 2021, the U.S. District for the Northern District of Alabama dismissed without prejudice a purported stockholder class action lawsuit, captioned Burbridge v. ADTRAN, Inc. et al, Docket No. 19-cv-09619 originally filed on October 17, 2019. This matter has been fully resolved by agreement among the parties, with no further action to be taken by the plaintiffs and each party bearing its own costs. 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 its Board of Directors. The derivative suit, which is purportedly brought on behalf of ADTRAN, claims that the defendants made 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. These are similar allegations as the shareholder class action that was dismissed without prejudice by the Court on March 31, 2021, and fully resolved by mutual agreement of the parties on May 3, 2021. The parties to the shareholder derivative suit agreed to a joint stipulation requesting a stay in the proceedings due to the resolution of the shareholder class action that remains in effect at least until May 19, 2021. The Company and its defendants disagree with the claims made in the complaint, and the defendants intend to vigorously defend against this lawsuit. At this time, we are unable to predict the outcome of or estimate the possible loss or range of loss, if any, associated with this lawsuit. 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. 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 March 31, 2021 and December 31, 2020, we had commitments related to these bonds totaling $21.2 million and $15.2 million, respectively, which expire at various dates through August 2024. 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 $18.2 million as of March 31, 2021, of which $0.1 million is included in restricted cash and $18.1 million is included in long-term investments on the Condensed Consolidated Balance Sheet. 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 March 31, 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 applied as of March 31, 2021.

Commitments and Contingencies

3 Months Ended

Mar. 31, 2021

Commitments And Contingencies Disclosure [Abstract]

19. COMMITMENTS AND CONTINGENCIES

Securities Class Action Lawsuit

On March 31, 2021, the U.S. District for the Northern District of Alabama dismissed without prejudice a purported stockholder class action lawsuit, captioned Burbridge v. ADTRAN, Inc. et al, Docket No. 19-cv-09619 originally filed on October 17, 2019. This matter has been fully resolved by agreement among the parties, with no further action to be taken by the plaintiffs and each party bearing its own costs.

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 its Board of Directors. The derivative suit, which is purportedly brought on behalf of ADTRAN, claims that the defendants made 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. These are similar allegations as the shareholder class action that was dismissed without prejudice by the Court on March 31, 2021, and fully resolved by mutual agreement of the parties on May 3, 2021. The parties to the shareholder derivative suit agreed to a joint stipulation requesting a stay in the proceedings due to the resolution of the shareholder class action that remains in effect at least until May 19, 2021. The Company and its defendants disagree with the claims made in the complaint, and the defendants intend to vigorously defend against this lawsuit. At this time, we are unable to predict the outcome of or estimate the possible loss or range of loss, if any, associated with this lawsuit.

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.

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 March 31, 2021 and December 31, 2020, we had commitments related to these bonds totaling $21.2 million and $15.2 million, respectively, which expire at various dates through August 2024. 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 $18.2 million as of March 31, 2021, of which $0.1 million is included in restricted cash and $18.1 million is included in long-term investments on the Condensed Consolidated Balance Sheet. 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 March 31, 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 applied as of March 31, 2021.