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Alabama State Industrial Development Authority Financing and Economic Incentives - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Jan. 02, 2020
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2008
Jan. 13, 1995
Debt Instrument [Line Items]            
Proceeds from state industrial development authority issued taxable bonds loaned to ADTRAN     $ 24,600      
Repayment of bond   $ 24,600        
Payments on long-term debt     1,000 $ 1,100    
Total economic incentives realized   $ 0 1,200 $ 1,400    
Taxable Revenue Bonds [Member]            
Debt Instrument [Line Items]            
Proceeds from state industrial development authority issued taxable bonds loaned to ADTRAN     24,600   $ 50,000 $ 20,000
Percentage of interest on bond   2.00%        
Maturity date of bond   Jan. 01, 2020        
Repayment of bond $ 24,600          
Certificate of deposit     25,600      
Payments on long-term debt     $ 1,000