Stockholders' Equity - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended	6 Months Ended
	Oct. 31, 2012	Jun. 30, 2013	Jun. 30, 2013
Stock Repurchase Program [Line Items]
Aggregate amount of common stock authorized for repurchase	$ 300.0
Treasury stock acquired		$ 8.8	$ 40.4
Treasury stock, shares, acquired		23,409	113,160
Treasury stock acquired, average cost per share		$ 376.49	$ 356.92