Segment Information - Segment Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Total sales	$ 772,031	$ 818,594
Income (loss) from operations	142,181	148,420
Interest expense and other, net	(4,717)	(7,172)
Income from operations before income taxes	137,464	141,248
Freight Segment
Segment Reporting Information [Line Items]
Total sales	442,669	511,887
Income (loss) from operations	106,675	111,569
Interest expense and other, net	0	0
Income from operations before income taxes	106,675	111,569
Transit Segment
Segment Reporting Information [Line Items]
Total sales	329,362	306,707
Income (loss) from operations	45,010	41,423
Interest expense and other, net	0	0
Income from operations before income taxes	45,010	41,423
Operating Segments | Freight Segment
Segment Reporting Information [Line Items]
Total sales	448,477	520,815
Operating Segments | Transit Segment
Segment Reporting Information [Line Items]
Total sales	331,039	309,291
Intersegment sales/(elimination)
Segment Reporting Information [Line Items]
Total sales	(7,485)	(11,512)
Intersegment sales/(elimination) | Freight Segment
Segment Reporting Information [Line Items]
Total sales	5,808	8,928
Intersegment sales/(elimination) | Transit Segment
Segment Reporting Information [Line Items]
Total sales	1,677	2,584
Corporate Activities and Elimination
Segment Reporting Information [Line Items]
Total sales	(7,485)	(11,512)
Income (loss) from operations	(9,504)	(4,572)
Interest expense and other, net	(4,717)	(7,172)
Income from operations before income taxes	$ (14,221)	$ (11,744)