Earnings per Share - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Earnings Per Share Disclosure [Line Items]
Options to purchase shares of common stock, incremental shares excluded from the computation of diluted EPS	2,834,487	697,994
Options to purchase shares of common stock, weighted average exercise price of incremental shares excluded from the computation of diluted EPS	$ 66.51	$ 67.64