Cash and cash equivalents (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Cash and cash equivalents:
Cash	$ 18,288		$ 3,247
Money market accounts	2,230		5,602
Total cash and cash equivalents	20,518	$ 7,954	8,849	$ 27,338
Short-term marketable securities:
Money market accounts			1,614
Total short-term marketable securities	0		$ 1,614
Interest and other income (expense), net
Short-term marketable securities:
Interest income	$ 4	$ 86