Unrecognized Share Based Compensation Expense (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized share-based compensation expense	$ 7.4
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized share-based compensation expense	1.2
Weighted average years expected to recognize compensation (in years)	2 years 5 months
Performance-Based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized share-based compensation expense	1.7
Weighted average years expected to recognize compensation (in years)	2 years 5 months
Time-Based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized share-based compensation expense	$ 4.5
Weighted average years expected to recognize compensation (in years)	1 year 7 months