Cash and cash equivalents and marketable securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash and cash equivalents:
Cash	$ 12,488	$ 3,247
Money market accounts	2,230	5,602
Total cash and cash equivalents	14,718	8,849	$ 27,338	$ 58,138
Short-term marketable securities:
Marketable securities	0	1,614
Total short-term marketable securities	0	1,614
Interest income	$ 66	$ 114	$ 181