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Alabama State Industrial Development Authority Financing and Economic Incentives - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2008
Jan. 13, 1995
Debt Instrument [Line Items]          
Proceeds from state industrial development authority issued taxable bonds loaned to ADTRAN $ 26,700     $ 50,000 $ 20,000
Percentage of interest on amended and restated bond 2.00%        
Maturity date of amended and restated bond Jan. 01, 2020        
Estimated fair value of bond $ 26,700        
Restricted certificate of deposit held 27,800 $ 27,800      
Total realized economic incentives 1,500 1,300 $ 1,300    
Payments on long-term debt 1,100 $ 1,100 $ 1,100    
Bond debt outstanding classified as current liability 1,100        
Significant Other Observable Inputs (Level 2) [Member]          
Debt Instrument [Line Items]          
Estimated fair value of bond $ 26,700