Other current assets (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid expenses	$ 1,534	$ 2,287
Security deposits and other receivables	836	551
Interest receivable	134	237
Other current assets	2,504	3,075
Deposits paid for research and development	$ 3,100	$ 2,000