Goodwill and Other Intangible Assets - Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 82,554
Goodwill, ending balance	117,435
Electronic Systems
Goodwill [Line Items]
Gross goodwill		$ 164,276
Accumulated goodwill impairment		$ (81,722)
Goodwill [Roll Forward]
Goodwill, beginning balance	82,554
Goodwill from acquisition during the period	34,881
Goodwill, ending balance	$ 117,435