Stockholders' Equity - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Stockholders Equity Note [Line Items]
Stock-based compensation expense	$ 2.6	$ 2.6	$ 11.0	$ 11.1
Stock-based compensation expense realized tax benefits from the excess of deductible amounts over expense recognized			$ 0.8	$ 0.7
Additional common shares issued under deferred and stock compensation arrangements			447,002