Earnings per Share - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Earnings Per Share Disclosure [Line Items]
Options to purchase shares of common stock, incremental shares excluded from the computation of diluted EPS	1,823,564	2,220,567	1,793,905
Options to purchase shares of common stock, weighted average exercise price of incremental shares excluded from the computation of diluted EPS	$ 69.46	$ 58.78	$ 56.25