Share Based Awards - Options by price (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of shares outstanding	11,498,747
Weighted average remaining contractual term, outstanding	6 years 10 months 10 days
Weighted average exercise price, outstanding	$ 4.51
Number of shares exercisable	7,167,464
Weighted average exercise price, exercisable	$ 3.55
Vested options exercised, intrinsic value	$ 11.8	$ 5.4	$ 1.8
Options granted, grant date fair value per share	$ 3.04	$ 4.09	$ 2.46
$0.04 - $1.75
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price, lower limit	0.04
Exercise price, upper limit	$ 1.75
Number of shares outstanding	2,360,113
Weighted average remaining contractual term, outstanding	5 years 15 days
Weighted average exercise price, outstanding	$ 1.07
Number of shares exercisable	2,356,759
Weighted average exercise price, exercisable	$ 1.07
$2.90 - $3.70
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price, lower limit	2.90
Exercise price, upper limit	$ 3.70
Number of shares outstanding	2,683,361
Weighted average remaining contractual term, outstanding	6 years 1 month 2 days
Weighted average exercise price, outstanding	$ 3.58
Number of shares exercisable	2,146,702
Weighted average exercise price, exercisable	$ 3.58
$3.77 - $5.77
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price, lower limit	3.77
Exercise price, upper limit	$ 5.77
Number of shares outstanding	3,938,687
Weighted average remaining contractual term, outstanding	7 years 3 months 26 days
Weighted average exercise price, outstanding	$ 5.02
Number of shares exercisable	1,920,743
Weighted average exercise price, exercisable	$ 4.83
$6.20 - $9.87
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price, lower limit	6.20
Exercise price, upper limit	$ 9.87
Number of shares outstanding	2,374,992
Weighted average remaining contractual term, outstanding	8 years 6 months 22 days
Weighted average exercise price, outstanding	$ 7.73
Number of shares exercisable	695,741
Weighted average exercise price, exercisable	$ 7.76
$10.80 - $12.05
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price, lower limit	10.80
Exercise price, upper limit	$ 12.05
Number of shares outstanding	141,594
Weighted average remaining contractual term, outstanding	8 years 6 months 11 days
Weighted average exercise price, outstanding	$ 11.31
Number of shares exercisable	47,519
Weighted average exercise price, exercisable	$ 11.33