Stock-Based Compensation - Summary of Changes in Stock Options Outstanding (Details) - Employee stock option - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2015	Sep. 30, 2015	Dec. 31, 2014
Number of Options (in shares):
Options outstanding at beginning of period	1.5	1.6	1.6	1.6
Granted	0.6	0.2
Exercised	(0.1)	(0.3)
Canceled	(0.1)	0.0
Options outstanding at end of period	1.9	1.5	1.9	1.9	1.6
Options exercisable at end of period				0.8
Options outstanding, weighted average remaining contract term (in years)		7 years 2 months 12 days	7 years 10 months 24 days	7 years 9 months 18 days	6 years 3 months 18 days
Options exercisable, Weighted average remaining contract term (in years)				5 years 8 months 12 days
Weighted average exercise price (in dollars per share):
Options outstanding at beginning of period	$ 11.78	$ 11.61	$ 11.61	$ 11.61
Granted	12.83	12.04
Exercised	9.10	9.83
Canceled	10.47
Options outstanding at end of period	$ 12.24	$ 11.78	$ 12.24	12.29	$ 11.61
Options exercisable at end of period				$ 11.25
Aggregate Intrinsic Value:
Options outstanding at beginning of period	$ 1.2	$ 4.0	$ 4.0	$ 4.0
Exercised	0.0	0.0
Options outstanding at end of period	$ 7.1	$ 1.2	$ 7.1	1.0	$ 4.0
Options exercisable at end of period				$ 0.8