Other balance sheet items - Schedule of Prepayments and Other Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Advances to suppliers		$ 8,028	$ 6,509
Prepaid income taxes		10,674	10,935
Prepaid other taxes		10,155	10,737
Contract deposit		2,700	2,700
Favorable ground lease asset		2,631	0
Other assets		2,039	3,185
Total prepayments and other assets		36,227	$ 34,066
Schedule of Equity Method Investments [Line Items]
Additional amount due that will be treated as key money if purchase not completed		$ 800
Forecast
Schedule of Equity Method Investments [Line Items]
Ownership interest planning to purchase	30.00%