Schedule Of Additional Information On Unvested Options (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	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]
Number of shares outstanding	391,700	327,000	237,150	203,250
Weighted-average remaining contractual term (in years)	3 years 8 months 19 days	2 years 11 months 12 days
Aggregate intrinsic value	$ 99,212	$ 94,270
Unvested Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	3,070,320	3,354,575
Weighted-average exercise price (per share)	$ 41.98	$ 33.30
Weighted-average remaining contractual term (in years)	5 years 8 months 12 days	5 years 6 months 18 days
Aggregate intrinsic value	$ 29,740	$ 35,173