Variable interest entities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014
Variable Interest Entity, Not Primary Beneficiary | Peruvian rail joint venture
Schedule Of Unconsolidated Variable Interest Entity Asset Carrying Value and Maximum Exposure to Loss [Line Items]
Ownership percentage in variable interest entity	50.00%
Guarantor obligations, triggering event, ownership percentage falls below 50%	50.00%
Long-term debt default amount classified in current liabilities	$ 5,486
Variable Interest Entity, Not Primary Beneficiary | Financial Guarantee Additional Debt 2016 | Peruvian rail joint venture
Schedule Of Unconsolidated Variable Interest Entity Asset Carrying Value and Maximum Exposure to Loss [Line Items]
Guarantor obligations, maximum exposure	5,486
Variable Interest Entity, Not Primary Beneficiary | Contingent Financial Guarantee Debt 2016 | Peruvian rail joint venture
Schedule Of Unconsolidated Variable Interest Entity Asset Carrying Value and Maximum Exposure to Loss [Line Items]
Guarantor obligations, maximum exposure	7,019
Variable Interest Entity, Not Primary Beneficiary | Guarantee of Governmental Concession | Peruvian rail joint venture
Schedule Of Unconsolidated Variable Interest Entity Asset Carrying Value and Maximum Exposure to Loss [Line Items]
Guarantor obligations, maximum exposure	$ 6,976
Charleston Center LLC | Variable Interest Entity, Primary Beneficiary
Schedule Of Unconsolidated Variable Interest Entity Asset Carrying Value and Maximum Exposure to Loss [Line Items]
Ownership percentage in variable interest entity	19.90%