Supplemental Balance Sheet Information - Other non-current assets (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Other non-current assets:
Prepayment of property and equipment	$ 6,306		$ 12,867
Tax on intra-entity contribution of subsidiary			28,588
Rental deposits and other	5,146		1,460
Total	$ 11,452	$ 14,327	$ 42,915