Other balance sheet items - Schedule of Other Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Tax contingencies	$ 2,347	$ 2,310
Pension obligations	5,368	4,456
Cap Cana land purchase obligation	10,625	10,625
Unfavorable ground lease liability	2,322	0
Other	1,811	2,003
Total other liabilities	$ 22,473	$ 19,394