Balance sheet components - Accrued and other current liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Transition services agreement payables (see Note 6)	$ 11,769		$ 11,769
Employee-related	12,905		14,899
Asset sale related contingent liabilities (see Note 6)	6,762		6,751
Operating lease liabilities, current	2,223
Accrued warranty	751	$ 739	672	$ 1,592	$ 1,699	$ 1,334
Deferred revenue, current	291		1,114
Income and other taxes payable	1,107		1,580
Rusnano payment derivative	0		2,000
Accrued litigation settlement	0		2,645
Other accrued expenses	7,212		8,858
Accrued and other current liabilities	$ 43,020		$ 50,288