Property, plant and equipment - Major classes of property, plant and equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, plant and equipment
Property, plant and equipment, gross	$ 1,585,782	$ 1,443,615
Less: Accumulated depreciation	(417,738)	(368,939)
Total property, plant and equipment, net of accumulated depreciation	1,168,044	1,074,676
Land and buildings
Property, plant and equipment
Property, plant and equipment, gross	1,126,496	1,010,362
Machinery and equipment
Property, plant and equipment
Property, plant and equipment, gross	181,670	179,537
Furniture, fixtures and equipment
Property, plant and equipment
Property, plant and equipment, gross	263,716	235,098
River cruise ship and canal boats
Property, plant and equipment
Property, plant and equipment, gross	$ 13,900	$ 18,618