Segment Information - Segment Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Total sales	$ 1,077,814	$ 957,931	$ 3,245,671	$ 2,806,218
Income (loss) from operations	125,179	101,666	379,981	329,535
Interest expense and other, net	(22,512)	(20,481)	(69,959)	(52,156)
Income from operations before income taxes	102,667	81,185	310,022	277,379
Freight Segment
Segment Reporting Information [Line Items]
Total sales	391,577	340,185	1,183,389	1,032,959
Income from operations before income taxes	79,420	61,424	233,390	195,811
Transit Segment
Segment Reporting Information [Line Items]
Total sales	686,237	617,746	2,062,282	1,773,259
Income from operations before income taxes	60,735	47,358	186,794	155,383
Operating Segments | Freight Segment
Segment Reporting Information [Line Items]
Total sales	405,087	348,561	1,227,600	1,060,561
Income (loss) from operations	79,420	61,424	233,390	195,811
Interest expense and other, net	0	0	0	0
Operating Segments | Transit Segment
Segment Reporting Information [Line Items]
Total sales	690,975	622,240	2,073,893	1,789,512
Income (loss) from operations	60,735	47,358	186,794	155,383
Interest expense and other, net	0	0	0	0
Intersegment sales/(elimination)
Segment Reporting Information [Line Items]
Total sales	(18,248)	(12,870)	(55,822)	(43,855)
Intersegment sales/(elimination) | Freight Segment
Segment Reporting Information [Line Items]
Total sales	13,510	8,376	44,211	27,602
Intersegment sales/(elimination) | Transit Segment
Segment Reporting Information [Line Items]
Total sales	4,738	4,494	11,611	16,253
Corporate Activities and Elimination
Segment Reporting Information [Line Items]
Income (loss) from operations	(14,976)	(7,116)	(40,203)	(21,659)
Interest expense and other, net	(22,512)	(20,481)	(69,959)	(52,156)
Income from operations before income taxes	$ (37,488)	$ (27,597)	$ (110,162)	$ (73,815)