Business Combination Agreement	12 Months Ended
Dec. 31, 2021
Business Combinations [Abstract]
Business Combination Agreement	Note 3 – Business Combination Agreement On August 30, 2021, the Company and 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, 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 has also made 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. On January 6, 2022, the Company's stockholders approved the Business Combination by an overwhelming majority. The end of the ADVA shareholder tender offer acceptance period was on January 26, 2022, which resulted in the acceptance of the Exchange Offer by more than 60% of all shares of ADVA entitled to voting rights existing as of October 31, 2021, thus exceeding the required minimum acceptance threshold. According to the rules of the German Securities Acquisition and Takeover Act, ADVA shareholders who did not tender their shares during the initial acceptance period could do so during a two-week additional acceptance period that began on February 1, 2022 and ended February 14, 2022. This resulted in the acceptance of the Exchange Offer by approximately 66% of all shares of ADVA entitled to voting rights existing as of November 30, 2021. On January 24, 2022, the Committee on Foreign Investment in the United States ("CFIUS") completed its review of the Business Combination and determined that the transaction was not a “covered transaction” subject to CFIUS’ jurisdiction, satisfying the condition of the Business Combination Agreement related to CFIUS notification. On February 16, 2022, the U.K. Secretary of State for Business, Energy and Industrial Strategy completed its review of the Business Combination and determined that the Secretary of State will be taking no further action under the NS&I Act, satisfying the condition of the Business Combination Agreement related to NS&I Act approval. Cooperative proceedings continue with the foreign direct investment authorities in Germany. The Company anticipates the consummation of the Business Combination around the middle of 2022, subject to customary closing conditions, and regulatory approvals from the foreign direct investment authorities in Germany. 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 was declared effective December 2, 2021 (the “Acorn HoldCo Registration Statement”).

Business Combination Agreement

12 Months Ended

Dec. 31, 2021

Note 3 – Business Combination Agreement

On August 30, 2021, the Company and 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, 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 has also made 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. On January 6, 2022, the Company's stockholders approved the Business Combination by an overwhelming majority. The end of the ADVA shareholder tender offer acceptance period was on January 26, 2022, which resulted in the acceptance of the Exchange Offer by more than 60% of all shares of ADVA entitled to voting rights existing as of October 31, 2021, thus exceeding the required minimum acceptance threshold. According to the rules of the German Securities Acquisition and Takeover Act, ADVA shareholders who did not tender their shares during the initial acceptance period could do so during a two-week additional acceptance period that began on February 1, 2022 and ended February 14, 2022. This resulted in the acceptance of the Exchange Offer by approximately 66% of all shares of ADVA entitled to voting rights existing as of November 30, 2021. On January 24, 2022, the Committee on Foreign Investment in the United States ("CFIUS") completed its review of the Business Combination and determined that the transaction was not a “covered transaction” subject to CFIUS’ jurisdiction, satisfying the condition of the Business Combination Agreement related to CFIUS notification. On February 16, 2022, the U.K. Secretary of State for Business, Energy and Industrial Strategy completed its review of the Business Combination and determined that the Secretary of State will be taking no further action under the NS&I Act, satisfying the condition of the Business Combination Agreement related to NS&I Act approval. Cooperative proceedings continue with the foreign direct investment authorities in Germany.

The Company anticipates the consummation of the Business Combination around the middle of 2022, subject to customary closing conditions, and regulatory approvals from the foreign direct investment authorities in Germany.

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 was declared effective December 2, 2021 (the “Acorn HoldCo Registration Statement”).