Stock-based compensation and awards (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Summary of stock awards outstanding and exercisable
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Number of outstanding options	4,882,111	4,505,153
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Outstanding options, Weighted average remaining contractual term	7 years 6 months	7 years 9 months 18 days
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Outstanding options, Weighted average exercise price	$ 5.98	$ 4.25
Share-based compensation arrangement by share-based payment award, Options, Outstanding, Intrinsic value	$ 12,323	$ 43,005
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Number exercisable	2,432,898	2,145,746
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Exercisable options, Weighted average remaining contractual term	6 years 2 months 12 days	6 years 8 months 12 days
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Exercisable options, Weighted average exercise price	$ 2.79	$ 2.76
Share-based compensation arrangement by share-based payment award, Options, Exercisable, Intrinsic value	$ 9,257	$ 23,689
Range One [Member]
Summary of stock awards outstanding and exercisable
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Lower range limit	$ 0.60	$ 0.60
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Upper range limit	$ 0.90	$ 0.90
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Number of outstanding options	711,648	755,519
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Outstanding options, Weighted average remaining contractual term	3 years 6 months	4 years 2 months 12 days
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Outstanding options, Weighted average exercise price	$ 0.72	$ 0.72
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Number exercisable	711,664	753,126
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Exercisable options, Weighted average remaining contractual term	3 years 6 months	4 years 2 months 12 days
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Exercisable options, Weighted average exercise price	$ 0.72	$ 0.72
Range Two [Member]
Summary of stock awards outstanding and exercisable
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Lower range limit	$ 2.40	$ 2.40
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Upper range limit	$ 3.00	$ 3.00
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Number of outstanding options	2,054,633	2,285,729
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Outstanding options, Weighted average remaining contractual term	7 years 2 months 12 days	8 years
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Outstanding options, Weighted average exercise price	$ 2.57	$ 2.54
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Number exercisable	1,356,049	1,107,324
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Exercisable options, Weighted average remaining contractual term	7 years	7 years 8 months 12 days
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Exercisable options, Weighted average exercise price	$ 2.52	$ 2.48
Range Three [Member]
Summary of stock awards outstanding and exercisable
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Lower range limit	$ 3.30	$ 3.30
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Upper range limit	$ 5.10	$ 5.10
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Number of outstanding options	497,361	556,829
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Outstanding options, Weighted average remaining contractual term	8 years 3 months 18 days	9 years
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Outstanding options, Weighted average exercise price	$ 4.27	$ 4.24
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Number exercisable	189,148	87,068
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Exercisable options, Weighted average remaining contractual term	8 years 3 months 18 days	9 years
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Exercisable options, Weighted average exercise price	$ 4.28	$ 3.69
Range Four [Member]
Summary of stock awards outstanding and exercisable
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Lower range limit	$ 7.17	$ 9.30
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Upper range limit	$ 13.80	$ 11.70
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Number of outstanding options	1,290,813	907,076
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Outstanding options, Weighted average remaining contractual term	9 years 2 months 12 days	9 years 9 months 18 days
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Outstanding options, Weighted average exercise price	$ 11.65	$ 11.53
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Number exercisable	173,539	198,228
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Exercisable options, Weighted average remaining contractual term	9 years 1 month 6 days	9 years 9 months 18 days
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Exercisable options, Weighted average exercise price	$ 11.65	$ 11.67
Range Five [Member]
Summary of stock awards outstanding and exercisable
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Lower range limit	$ 15.30
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Upper range limit	$ 21.88
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Number of outstanding options	327,656
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Outstanding options, Weighted average remaining contractual term	9 years 8 months 12 days
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Outstanding options, Weighted average exercise price	$ 19.04
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Number exercisable	2,514
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Exercisable options, Weighted average remaining contractual term	9 years 7 months 6 days
Share-based compensation, Shares authorized under stock option plans, Exercise price range, Exercisable options, Weighted average exercise price	$ 16.55