Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		27 Months Ended	39 Months Ended	45 Months Ended	51 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2009	Dec. 31, 2010	Jun. 30, 2011	Dec. 31, 2011
Income Tax Disclosure [Abstract]
Effective income tax rates	23.70%	22.60%	23.50%	21.20%
Impact of the expiration of the U.S. federal research and development tax credit		1.80%		1.80%
Prior period reclassification adjustment to decrease deferred tax liability and increase additional paid-in capital					$ 499.6	$ 467.1	$ 407.2	$ 352.6