Supplemental Balance Sheet Information - Other long-term liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Other long-term liabilities
Deferred government grant income	$ 21,449		$ 31,804
Other	323		155
Total other long-term liabilities	$ 21,772	$ 21,969	$ 31,959