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, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Carrying Amounts, Total	$ 7,589	$ 7,844
Maximum exposure	7,589	7,844
Investment
Variable Interest Entity [Line Items]
Carrying Amounts, Assets	2,818	2,972
Maximum exposure	2,818	2,972
Due from unconsolidated company
Variable Interest Entity [Line Items]
Carrying Amounts, Assets	4,771	4,872
Maximum exposure	4,771	4,872
Guarantees
Variable Interest Entity [Line Items]
Carrying Amounts, Liabilities	0	0
Maximum exposure	0	0
Contingent guarantees
Variable Interest Entity [Line Items]
Carrying Amounts, Liabilities	0	0
Maximum exposure	$ 0	$ 0