Fair value measurement (Details) (Recurring basis, USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Level 1
Assets:
Money market accounts	$ 2,229	$ 5,602
Total assets	2,229	5,602
Level 2
Assets:
Marketable securities		1,614
Total assets		1,614
Level 3
Liabilities:
Contingent consideration	17	131
Total liabilities	17	131
Total
Assets:
Money market accounts	2,229	5,602
Marketable securities		1,614
Total assets	2,229	7,216
Liabilities:
Contingent consideration	17	131
Total liabilities	$ 17	$ 131