Derivative Financial Instruments (Details)	3 Months Ended							3 Months Ended
	Mar. 31, 2012 USD ($)	Mar. 31, 2011 USD ($)	Dec. 31, 2011 USD ($)	Dec. 01, 2010 USD ($)	Dec. 01, 2010 AUD	Oct. 02, 2008 USD ($)	Mar. 31, 2012 Cross-currency swap [Member] USD ($)	Mar. 31, 2012 AUD BBSW Interest Rate [Member] Cross-currency swap [Member]	Mar. 31, 2012 Libor Interest Rate [Member] Cross-currency swap [Member]	Mar. 31, 2012 Cross-currency swap [Member] USD ($)	Mar. 31, 2011 Cross-currency swap [Member] USD ($)	Dec. 01, 2010 FreightLink [Member] USD ($)	Dec. 01, 2010 FreightLink [Member] AUD
Derivatives [Line Items]
Notional amount of interest rate derivatives						$ 120,000,000
Fixed rate on notional amount of interest rate swap						3.88%
Liability derivatives	14,828,000		14,195,000
Gain (loss) reclassified from accumulated OCI into earnings	0
Third-party debt associated with foreign currency debt	209,100,000
Acquisition of assets												320,000,000	331,900,000
Intercompany loan				100,600,000	105,000,000
Derivative, description of variable rate basis								Australian dollar BBSW plus 3.125%	LIBOR plus 2.48%
Interest (expense)/income										(1,318,000)	(1,436,000)
Other income, net	984,000	568,000								173,000	22,000
Derivative liability, net							$ 8,500,000