Segment Information - Sales by Product (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Total sales	$ 1,056,177	$ 916,034
Specialty Products & Electronics
Segment Reporting Information [Line Items]
Total sales	386,548	315,067
Transit Products
Segment Reporting Information [Line Items]
Total sales	274,265	258,419
Brake Products
Segment Reporting Information [Line Items]
Total sales	215,618	180,459
Remanufacturing, Overhaul & Build
Segment Reporting Information [Line Items]
Total sales	135,713	129,058
Other
Segment Reporting Information [Line Items]
Total sales	$ 44,033	$ 33,031