Stock incentive plans (Details 4) (USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Number of Options
Outstanding at the beginning of the period (in shares)	4,955
Granted (in shares)	203
Exercised (in shares)	(203)
Canceled/forfeited (in shares)	(176)
Outstanding at the end of the period (in shares)	4,779	4,955
Vested, exercisable and expected to vest at the end of the period (in shares)	4,653
Exercisable at the end of the period (in shares)	2,919
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 6.31
Granted (in dollars per share)	$ 5.99
Exercised (in dollars per share)	$ 0.88
Canceled/forfeited (in dollars per share)	$ 8.28
Outstanding at the end of the period (in dollars per share)	$ 6.46	$ 6.31
Vested and expected to vest at the end of the period (in dollars per share)	$ 6.43
Exercisable at the end of the period (in dollars per share)	$ 5.27
Weighted-Average Remaining Contract Life (years)
Outstanding	6 years 3 months 18 days	6 years 7 months 6 days
Vested and expected to vest at the end of the period	6 years 3 months 18 days
Exercisable at the end of the period	5 years
Aggregate Intrinsic Value
Outstanding at the beginning of the period	$ 9,535
Outstanding at the end of the period	9,567	9,535
Vested and expected to vest at the end of the period	9,522
Exercisable at the end of the period	$ 9,005