Changes in Carrying Amount of Goodwill (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Goodwill [Line Items]
Balance at December 31, 2011	$ 587,531
Acquisition	34,951
Adjustment to preliminary purchase allocation	2,893
Foreign currency impact	(1,444)
Balance at June 30, 2012	623,931
Freight Segment [Member]
Goodwill [Line Items]
Balance at December 31, 2011	388,221
Adjustment to preliminary purchase allocation	1,901
Foreign currency impact	362
Balance at June 30, 2012	390,484
Transit Segment [Member]
Goodwill [Line Items]
Balance at December 31, 2011	199,310
Acquisition	34,951
Adjustment to preliminary purchase allocation	992
Foreign currency impact	(1,806)
Balance at June 30, 2012	$ 233,447