Stock-Based Compensation - Summary of Changes in Stock Options Outstanding (Details) (Employee stock option, USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Employee stock option
Number of Options (in shares):
Options outstanding at beginning of period	1.6
Granted		0.2
Exercised		(0.3)
Canceled		0
Options outstanding at end of period	1.5		1.6
Options exercisable at end of period	0.9
Options outstanding, weighted average remaining contract term (in years)	7 years 2 months 12 days		6 years 3 months 18 days
Options exercisable, Weighted average remaining contract term (in years)	5 years 10 months 24 days
Weighted average exercise price (in dollars per share):
Options outstanding at beginning of period	$ 11.61
Granted		$ 12.04
Exercised		$ 9.83
Canceled
Options outstanding at end of period	$ 11.78		$ 11.61
Options exercisable at end of period	$ 11.14
Aggregate Intrinsic Value:
Options outstanding at beginning of period	$ 4.0
Exercised		0
Options outstanding at end of period	0		4.0
Options exercisable at end of period	$ 0.9