Share-Based Compensation - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock option exercised			500,000	600,000
Cash received from stock option exercises			$ 3.3	$ 2.6
Common stock issued pursuant to the vesting of restricted stock units (RSUs)			93,000
Stock options granted			900,000	800,000
Stock vesting period			4 years
Stock option contractual life			10 years
Share-based compensation expense	2.9	1.7	5.3	3.4
Due to Changes in the Plan | Scenario, Previously Reported
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock option contractual life			7 years
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Unrecognized compensation cost	8.9		8.9
Unrecognized compensation cost, weighted average period of recognition			3 years 3 months 18 days
Stock vesting period			4 years	4 years
Share-based compensation expense			1.2	0.4
Restricted stock units granted			400,000	400,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Unrecognized compensation cost	16.2		16.2
Unrecognized compensation cost, weighted average period of recognition			2 years 9 months 18 days
Stock vesting period			4 years
Share-based compensation expense			4.1	3.0
Performance-based RSUs
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Unrecognized compensation cost	9.3		9.3
RSU with performance-based vesting requirements outstanding	500,000		500,000
Stock vesting period			5 years
Share-based compensation expense	$ 0		$ 0
Restricted stock units granted			500,000