Fair value measurement (Details) - Recurring basis - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Assets:
Money market accounts	$ 2,230	$ 5,602
Marketable securities		1,614
Total assets	2,230	7,216
Liabilities:
Contingent consideration		131
Total liabilities		131
Level 1
Assets:
Money market accounts	2,230	5,602
Total assets	$ 2,230	5,602
Level 2
Assets:
Marketable securities		1,614
Total assets		1,614
Level 3
Liabilities:
Contingent consideration		131
Total liabilities		$ 131