Cash and cash equivalents (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Cash and cash equivalents:
Cash	$ 8,390		$ 3,247
Money market accounts	2,229		5,602
Total cash and cash equivalents	10,619	13,516	8,849	27,338
Short-term marketable securities:
Money market accounts			1,614
Total short-term marketable securities	0		1,614
Interest income	$ 1	$ 48