Summary of Stock Option Information and Weighted Average Exercise Prices (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Number of shares
Number of stock options outstanding at beginning of period	19,299	23,265	25,285
Number of stock options granted	1,827	2,211	3,097
Number of stock options exercised	(6,312)	(5,977)	(4,761)
Number of stock options forfeited	(134)	(163)	(232)
Number of stock options canceled	(50)	(37)	(124)
Number of stock options outstanding at end of period	14,630	19,299	23,265
Number of stock options exercisable at end of period	10,971	14,359	16,630
Weighted Average Exercise Price
Weighted average exercise price of stock options outstanding at beginning of period	$ 20.30	$ 19.48	$ 18.45
Weighted average exercise price of stock options granted	$ 34.29	$ 26.38	$ 21.52
Weighted average exercise price of stock options exercised	$ 19.50	$ 19.34	$ 15.41
Weighted average exercise price of stock options forfeited	$ 27.13	$ 20.50	$ 19.29
Weighted average exercise price of stock options canceled	$ 20.02	$ 17.46	$ 17.73
Weighted average exercise price of stock options outstanding at end of period	$ 22.34	$ 20.30	$ 19.48
Weighted average exercise price of stock options exercisable at end of period	$ 20.03	$ 19.39	$ 19.30