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Goodwill (Detail) - USD ($) $ in Thousands	6 Months Ended
Goodwill (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jan. 01, 2017
Goodwill [Line Items]
Gross goodwill			$ 199,157
Accumulated goodwill impairment		$ (81,722)
Goodwill	$ 136,051	117,435
Goodwill from acquisition during the period	18,616
Electronic Systems
Goodwill [Line Items]
Gross goodwill			199,157
Accumulated goodwill impairment		(81,722)
Goodwill	117,435	117,435
Goodwill from acquisition during the period	0
Structural Systems
Goodwill [Line Items]
Gross goodwill			$ 0
Accumulated goodwill impairment		0
Goodwill	18,616	$ 0
Goodwill from acquisition during the period	$ 18,616