Business Segment Information - Segment Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Total Assets	$ 593,849	$ 515,429
Total Goodwill and Intangibles	234,720	184,127
Operating Segments | Structural Systems
Segment Reporting Information [Line Items]
Total Assets	207,413	175,580
Total Goodwill and Intangibles	3,063	3,745
Operating Segments | Electronic Systems
Segment Reporting Information [Line Items]
Total Assets	376,569	325,780
Total Goodwill and Intangibles	231,657	180,382
Corporate Administration
Segment Reporting Information [Line Items]
Total Assets	$ 9,867	$ 14,069