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
	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Employee stock option
Number of Options (in shares):
Options outstanding at beginning of period	2.0	1.9	2.6
Granted	0	0.2	0.4
Exercised	(0.1)	0	0
Canceled	(0.2)	(0.1)	(1.1)
Options outstanding at end of period	1.7	2.0	1.9	2.6
Options exercisable at end of period	0.9
Options outstanding, weighted average remaining contract term (in years)	7 years 1 month 6 days	7 years 4 months 24 days	7 years 8 months 12 days	4 years 2 months 12 days
Options exercisable, Weighted average remaining contract term (in years)	6 years 1 month 6 days
Weighted average exercise price (in dollars per share):
Options outstanding at beginning of period	$ 12.34	$ 12.62	$ 10.46
Granted	$ 0.00	$ 8.94	$ 16.03
Exercised	$ 9.11	$ 0.00	$ 0.00
Canceled	$ 17.36	$ 13.88	$ 9.04
Options outstanding at end of period	$ 11.71	$ 12.34	$ 12.62	$ 10.46
Options exercisable at end of period	$ 11.01
Aggregate Intrinsic Value:
Options outstanding at beginning of period	$ 2.3	$ 0	$ 17.8
Exercised	0	0	0
Options outstanding at end of period	1.8	2.3	0	17.8
Options exercisable at end of period	$ 1.1