Stock incentive plans (Details 4) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Number of Options
Outstanding at the beginning of the period (in shares)	4,341
Exercised (in shares)	(375)
Canceled/forfeited (in shares)	(135)
Outstanding at the end of the period (in shares)	3,831	4,341
Vested, exercisable and expected to vest at the end of the period (in shares)	3,801
Exercisable at the end of the period (in shares)	3,101
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 6.60
Exercised (in dollars per share)	3.32
Canceled/forfeited (in dollars per share)	9.82
Outstanding at the end of the period (in dollars per share)	6.80	$ 6.60
Vested and expected to vest at the end of the period (in dollars per share)	6.80
Exercisable at the end of the period (in dollars per share)	$ 6.51
Weighted-Average Remaining Contract Life (years)
Outstanding	5 years 2 months 12 days	5 years 9 months 18 days
Vested and expected to vest at the end of the period	5 years 2 months 12 days
Exercisable at the end of the period	4 years 8 months 12 days
Aggregate Intrinsic Value
Outstanding at the beginning of the period	$ 11,017
Outstanding at the end of the period	10,928	$ 11,017
Vested and expected to vest at the end of the period	10,879
Exercisable at the end of the period	$ 9,965