Stock Plans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for grants (in years)	4 years
Term of options outstanding (in years)	10 years
Unrecognized compensation cost expected to be recognized over the period (years)	4 years
Outstanding closing stock price per share	$ 31.82
Total number of available shares to grant	3,400,000
Options outstanding	2,091,000	4,450,000	5,316,000	7,289,000
Exercisable weighted average exercise price	$ 24.80