Segment Information - Segment Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Total sales	$ 957,931	$ 675,574	$ 2,806,218	$ 2,171,206
Income (loss) from operations	102,011	120,096	330,570	395,561
Interest expense and other, net	(20,826)	(4,869)	(53,191)	(15,784)
Income from operations before income taxes	81,185	115,227	277,379	379,777
Freight Segment
Segment Reporting Information [Line Items]
Total sales	340,185	361,998	1,032,959	1,201,734
Income from operations before income taxes	61,596	77,999	196,328	276,990
Transit Segment
Segment Reporting Information [Line Items]
Total sales	617,746	313,576	1,773,259	969,472
Income from operations before income taxes	47,531	51,164	155,901	148,321
Operating Segments | Freight Segment
Segment Reporting Information [Line Items]
Total sales	348,561	372,339	1,060,561	1,231,499
Income (loss) from operations	61,596	77,999	196,328	276,990
Interest expense and other, net	0	0	0	0
Operating Segments | Transit Segment
Segment Reporting Information [Line Items]
Total sales	622,240	315,399	1,789,512	977,078
Income (loss) from operations	47,531	51,164	155,901	148,321
Interest expense and other, net	0	0	0	0
Intersegment sales/(elimination)
Segment Reporting Information [Line Items]
Total sales	(12,870)	(12,164)	(43,855)	(37,371)
Intersegment sales/(elimination) | Freight Segment
Segment Reporting Information [Line Items]
Total sales	8,376	10,341	27,602	29,765
Intersegment sales/(elimination) | Transit Segment
Segment Reporting Information [Line Items]
Total sales	4,494	1,823	16,253	7,606
Corporate Activities and Elimination
Segment Reporting Information [Line Items]
Total sales	(12,870)	(12,164)	(43,855)	(37,371)
Income (loss) from operations	(7,116)	(9,067)	(21,659)	(29,750)
Interest expense and other, net	(20,826)	(4,869)	(53,191)	(15,784)
Income from operations before income taxes	$ (27,942)	$ (13,936)	$ (74,850)	$ (45,534)