Stock-Based Compensation Expense - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Employee stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense, net of estimated forfeitures	$ 41.8
Period to recognize total unrecognized compensation expense, net of estimated forfeitures on a weighted-average basis	2 years 7 months 6 days
Service-based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period to recognize total unrecognized compensation expense, net of estimated forfeitures on a weighted-average basis	3 years
Total unrecognized compensation expense, net of estimated forfeitures	124.0
Performance-based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to performance based awards, net of estimated forfeitures	$ 17.2
Period to recognize total unrecognized compensation expense, net of estimated forfeitures on a weighted-average basis	3 years