Segment Information - Segment Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Total sales	$ 723,601	$ 847,028	$ 1,495,632	$ 1,665,622
Income (loss) from operations	133,284	155,860	275,465	304,280
Interest expense and other, net	(6,198)	(5,928)	(10,915)	(13,100)
Income from operations before income taxes	127,086	149,932	264,550	291,180
Freight Segment
Segment Reporting Information [Line Items]
Total sales	410,683	543,703	859,160	1,064,518
Income from operations before income taxes	92,317	125,232	198,991	236,801
Transit Segment
Segment Reporting Information [Line Items]
Total sales	330,640	315,153	661,679	624,444
Income from operations before income taxes	52,146	37,514	97,156	78,937
Operating Segments | Freight Segment
Segment Reporting Information [Line Items]
Total sales	397,067	534,674	839,736	1,046,561
Income (loss) from operations	92,317	125,232	198,991	236,801
Interest expense and other, net	0	0	0	0
Operating Segments | Transit Segment
Segment Reporting Information [Line Items]
Total sales	326,534	312,354	655,896	619,061
Income (loss) from operations	52,146	37,514	97,156	78,937
Interest expense and other, net	0	0	0	0
Intersegment sales/(elimination)
Segment Reporting Information [Line Items]
Total sales	(17,722)	(11,828)	(25,207)	(23,340)
Intersegment sales/(elimination) | Freight Segment
Segment Reporting Information [Line Items]
Total sales	13,616	9,029	19,424	17,957
Intersegment sales/(elimination) | Transit Segment
Segment Reporting Information [Line Items]
Total sales	4,106	2,799	5,783	5,383
Corporate Activities and Elimination
Segment Reporting Information [Line Items]
Total sales	(17,722)	(11,828)	(25,207)	(23,340)
Income (loss) from operations	(11,179)	(6,886)	(20,682)	(11,458)
Interest expense and other, net	(6,198)	(5,928)	(10,915)	(13,100)
Income from operations before income taxes	$ (17,377)	$ (12,814)	$ (31,597)	$ (24,558)