Balance sheet components - Accrued and other current liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Transition services agreement payables (see Note 6)	$ 11,776	$ 11,769
Employee-related	17,504	14,899
Asset sale related contingent liabilities (see Note 6)	6,918	6,751
Operating lease liabilities, current	2,274
Accrued warranty	739	672	$ 1,699	$ 1,334
Deferred revenue, current	481	1,114
Income and other taxes payable	1,055	1,580
Rusnano payment derivative	2,000	2,000
Accrued litigation settlement	1,150	2,645
Other accrued expenses	6,372	8,858
Accrued and other current liabilities	$ 50,269	$ 50,288