Segment Information - Segment Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Segment Reporting Information [Line Items]
Total sales	$ 916,034	$ 772,031
Income (loss) from operations	114,858	142,181
Interest expense and other, net	(15,393)	(4,717)
Income from operations before income taxes	99,465	137,464
Freight Segment
Segment Reporting Information [Line Items]
Total sales	357,033	448,477
Income from operations before income taxes	71,395	106,675
Transit Segment
Segment Reporting Information [Line Items]
Total sales	573,774	331,039
Income from operations before income taxes	49,148	45,010
Operating Segments | Freight Segment
Segment Reporting Information [Line Items]
Total sales	347,946	442,669
Income (loss) from operations	71,395	106,675
Interest expense and other, net	0	0
Operating Segments | Transit Segment
Segment Reporting Information [Line Items]
Total sales	568,088	329,362
Income (loss) from operations	49,148	45,010
Interest expense and other, net	0	0
Intersegment sales/(elimination)
Segment Reporting Information [Line Items]
Total sales	(14,773)	(7,485)
Intersegment sales/(elimination) | Freight Segment
Segment Reporting Information [Line Items]
Total sales	9,087	5,808
Intersegment sales/(elimination) | Transit Segment
Segment Reporting Information [Line Items]
Total sales	5,686	1,677
Corporate Activities and Elimination
Segment Reporting Information [Line Items]
Total sales	(14,773)	(7,485)
Income (loss) from operations	(5,685)	(9,504)
Interest expense and other, net	(15,393)	(4,717)
Income from operations before income taxes	$ (21,078)	$ (14,221)