Stock Options - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of unissued common stock available for grant under the plans	2.4
Share-based compensation expense	$ 9.3	$ 8.9
Cash received from stock options exercised	2.8	1.2
Performance-Based Unit | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares which will vest after achievement of goals	0
Performance-Based Unit | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares which will vest after achievement of goals	1.5
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	3.2	3.1
Total unrecognized compensation cost	10.8
Unrecognized compensation cost, Weighted-average recognition period	2 years 7 months 6 days
Aggregate weighted-average grant-date fair value of units granted	12.7	4.9
Aggregate weighted-average grant-date fair value of units vested	2.7	4.3
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	6.1	5.8
Total intrinsic value of options exercised	4.6	2.1
Total unrecognized compensation cost	$ 5.1
Unrecognized compensation cost, Weighted-average recognition period	2 years