Balance sheet components - Restricted Cash and Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash and investments	$ 10,972	$ 11,053
Restricted cash	10,972	11,053
Restricted in connection with asset purchase agreement
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash and investments	1,999	2,019
Restricted in connection with notes payable and short-term borrowing
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash and investments	2,559	2,589
APAT OE Legal Dispute
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash and investments	5,989
APAT OE Legal Dispute | APAT OE Legal Dispute
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash and investments		5,156
Advances, Government Grants Received
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash and investments	$ 425	$ 1,289