Segment Information - Segment Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Total sales	$ 932,253	$ 723,601	$ 1,848,287	$ 1,495,632
Income (loss) from operations	113,701	133,284	228,559	275,465
Interest expense and other, net	(16,972)	(6,198)	(32,365)	(10,915)
Income from operations before income taxes	96,729	127,086	196,194	264,550
Freight Segment
Segment Reporting Information [Line Items]
Total sales	354,967	410,683	712,000	859,160
Income from operations before income taxes	63,337	92,317	134,732	198,991
Transit Segment
Segment Reporting Information [Line Items]
Total sales	593,498	330,640	1,167,272	661,679
Income from operations before income taxes	59,222	52,146	108,370	97,156
Operating Segments | Freight Segment
Segment Reporting Information [Line Items]
Total sales	344,828	397,067	692,774	839,736
Income (loss) from operations	63,337	92,317	134,732	198,991
Interest expense and other, net	0	0	0	0
Operating Segments | Transit Segment
Segment Reporting Information [Line Items]
Total sales	587,425	326,534	1,155,513	655,896
Income (loss) from operations	59,222	52,146	108,370	97,156
Interest expense and other, net	0	0	0	0
Intersegment sales/(elimination)
Segment Reporting Information [Line Items]
Total sales	(16,212)	(17,722)	(30,985)	(25,207)
Intersegment sales/(elimination) | Freight Segment
Segment Reporting Information [Line Items]
Total sales	10,139	13,616	19,226	19,424
Intersegment sales/(elimination) | Transit Segment
Segment Reporting Information [Line Items]
Total sales	6,073	4,106	11,759	5,783
Corporate Activities and Elimination
Segment Reporting Information [Line Items]
Total sales	(16,212)	(17,722)	(30,985)	(25,207)
Income (loss) from operations	(8,858)	(11,179)	(14,543)	(20,682)
Interest expense and other, net	(16,972)	(6,198)	(32,365)	(10,915)
Income from operations before income taxes	$ (25,830)	$ (17,377)	$ (46,908)	$ (31,597)