Computations of Basic and Diluted Earnings Per Share (Detail) (USD $) In Millions, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Earnings Per Share Disclosure [Line Items]
Net earnings	$ 65.4	$ 41.0	$ 170.5	$ 112.1
Basic weighted average common shares	101.0	99.7	100.9	99.5
Effect of dilutive stock options and employee stock purchase plan shares	0.1	0.1	0.1	0.1
Effect of restricted shares issued	0.9	1.2	0.8	1.1
Diluted weighted average common shares	102.0	101.0	101.8	100.7
Basic net earnings per share	$ 0.65	$ 0.41	$ 1.69	$ 1.13
Diluted net earnings per share	$ 0.64	$ 0.41	$ 1.67	$ 1.11