Cash and cash equivalents (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Cash and cash equivalents:
Cash	$ 6,326		$ 3,247
Money market accounts	2,230		5,602
Total cash and cash equivalents	8,556	$ 4,030	8,849	$ 27,338
Short-term marketable securities:
Marketable securities	0		1,614
Total short-term marketable securities			$ 1,614
Interest and other income (expense), net
Short-term marketable securities:
Interest income	$ 4	$ 105