Fair value measurement (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Assets:
Restricted cash	$ 545	$ 545
Recurring basis | Level 1
Assets:
Cash equivalents	4,295	23,683
Restricted cash	545	545
Total assets	4,840	24,228
Recurring basis | Level 2
Assets:
Marketable securities	29,909	32,962
Total assets	29,909	32,962
Recurring basis | Level 3
Liabilities:
Contingent consideration	1,584	1,942
Total liabilities	1,584	1,942
Recurring basis | Total
Assets:
Cash equivalents	4,295	23,683
Marketable securities	29,909	32,962
Restricted cash	545	545
Total assets	34,749	57,190
Liabilities:
Contingent consideration	1,584	1,942
Total liabilities	$ 1,584	$ 1,942