Balance sheet components - Accrued and other current liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Accrued and other current liabilities
Employee-related	$ 11,616	$ 17,420
Income and other taxes payable	2,233	3,720
Accrued warranty	1,143	1,175	$ 1,647	$ 1,751
Penalty payment derivative	389	389
Other accrued expenses	5,975	5,246
Accrued and other current liabilities	$ 21,356	$ 27,950