Business Segment Information - Segment Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total Assets	$ 631,893	$ 566,753
Total Goodwill and Intangibles	253,536	232,128
Operating Segments | Structural Systems
Segment Reporting Information [Line Items]
Total Assets	216,104	193,600
Total Goodwill and Intangibles	28,954	2,836
Operating Segments | Electronic Systems
Segment Reporting Information [Line Items]
Total Assets	402,206	362,831
Total Goodwill and Intangibles	224,582	229,292
Corporate Administration
Segment Reporting Information [Line Items]
Total Assets	$ 13,583	$ 10,322