Property, plant and equipment - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	$ 2,096,908	$ 1,749,727
Accumulated depreciation	(312,241)	(283,401)
Total property, plant and equipment, net	1,784,667	1,466,326
Land, buildings and improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	1,787,043	1,493,407
Fixtures and machinery
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	55,537	53,188
Furniture and other fixed assets
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	205,086	173,912
Construction in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	$ 49,242	$ 29,220