Business Segment Information - Segment Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Total Assets	$ 566,753	$ 515,429
Goodwill and Intangibles	232,128	184,127
Operating Segments | Structural Systems
Segment Reporting Information [Line Items]
Total Assets	193,600	175,580
Goodwill and Intangibles	2,836	3,745
Operating Segments | Electronic Systems
Segment Reporting Information [Line Items]
Total Assets	362,831	325,780
Goodwill and Intangibles	229,292	180,382
Corporate Administration
Segment Reporting Information [Line Items]
Total Assets	$ 10,322	$ 14,069