Variable interest entities - Carrying amounts and maximum exposure to loss for E&O joint venture (Details) - Eastern and Oriental Express Ltd. - Variable interest entity, not primary beneficiary - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity
Carrying Amounts, Total	$ 8,944	$ 7,589
Maximum exposure	8,944	7,589
Investment
Variable Interest Entity
Carrying Amounts, Assets	2,642	2,818
Maximum exposure	2,642	2,818
Due from unconsolidated company
Variable Interest Entity
Carrying Amounts, Assets	6,302	4,771
Maximum exposure	6,302	4,771
Guarantees
Variable Interest Entity
Carrying Amounts, Liabilities	0	0
Maximum exposure	0	0
Contingent guarantees
Variable Interest Entity
Carrying Amounts, Liabilities	0	0
Maximum exposure	$ 0	$ 0