Other current assets (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid expenses	$ 928	$ 2,287
Security deposits and other receivables	516	551
Interest receivable	282	237
Other current assets	1,726	3,075
Deposits paid for research and development	$ 2,400	$ 2,000