Segment Information - Sales by Product (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Total sales	$ 1,111,680	$ 932,253	$ 2,167,857	$ 1,848,287
Specialty Products & Electronics
Segment Reporting Information [Line Items]
Total sales	434,399	324,798	820,947	639,863
Transit Products
Segment Reporting Information [Line Items]
Total sales	282,130	253,764	556,409	512,182
Brake Products
Segment Reporting Information [Line Items]
Total sales	217,574	192,557	433,192	373,016
Remanufacturing, Overhaul & Build
Segment Reporting Information [Line Items]
Total sales	127,202	126,556	262,900	255,616
Other
Segment Reporting Information [Line Items]
Total sales	$ 50,375	$ 34,578	$ 94,409	$ 67,610