Financial Data of Business Segments - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2012
Rail [Member]
Operating Statistics [Line Items]
Leverage level expressed as a ratio of recourse debt to equity	4.0
ASC [Member]
Operating Statistics [Line Items]
Leverage level expressed as a ratio of recourse debt to equity	1.5
Portfolio Management [Member]
Operating Statistics [Line Items]
Leverage level expressed as a ratio of recourse debt to equity	3.0