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Goodwill (Detail) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Jan. 01, 2017
Goodwill [Line Items]      
Goodwill $ 117,435 $ 117,435  
Electronic Systems      
Goodwill [Line Items]      
Gross goodwill     $ 199,157
Accumulated goodwill impairment (81,722)    
Goodwill $ 117,435 $ 117,435