Other balance sheet items - Schedule of Other Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Tax contingencies	$ 2,347	$ 2,310
Pension obligations	4,936	4,456
Cap Cana land purchase obligation	10,625	10,625
Unfavorable ground lease liability	2,334	0
Other	1,785	2,003
Total other liabilities	$ 22,027	$ 19,394