Balance sheet components (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Restricted Cash And Cash Equivalents Items [Line Items]
Total restricted cash and investments	$ 3,062	$ 21,254
Restricted cash and investments	3,062	5,504
Restricted cash and investments, non-current		15,750
Notes Payable
Restricted Cash And Cash Equivalents Items [Line Items]
Total restricted cash and investments	$ 3,062	3,754
Comerica Bank Term Loan [Member]
Restricted Cash And Cash Equivalents Items [Line Items]
Total restricted cash and investments		$ 17,500