Stockholders' Equity - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Stockholders Equity Note [Line Items]
Stock-based compensation expense	$ 2.9	$ 2.7	$ 10.4	$ 8.5
Stock-based compensation expense realized tax benefits from the excess of deductible amounts over expense recognized	$ 0.2	$ 0.9	$ 1.5	$ 1.6
Additional common shares issued under deferred and stock compensation arrangements			452,658