Business Segment Information - Segment Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total Assets	$ 597,569	$ 566,753
Total Goodwill and Intangibles	229,589	232,128
Operating Segments | Structural Systems
Segment Reporting Information [Line Items]
Total Assets	195,443	193,600
Total Goodwill and Intangibles	2,652	2,836
Operating Segments | Electronic Systems
Segment Reporting Information [Line Items]
Total Assets	391,093	362,831
Total Goodwill and Intangibles	226,937	229,292
Corporate Administration
Segment Reporting Information [Line Items]
Total Assets	$ 11,033	$ 10,322