Leases - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2015 Scenario, Forecast Railroad Equipment	Dec. 31, 2014 Scenario, Forecast Railroad Equipment
Schedule of Operating Leases [Line Items]
Sublease income	$ 208			$ 1,619	$ 1,985
Rent expense for all operating leases	$ 22,542	$ 21,452	$ 11,590