Summary of Information Regarding Stock Options (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Number of Options
Beginning Balance	2,326,776
Granted	329,500
Exercised	(834,545)
Forfeited	(20,800)
Ending Balance	1,800,931
Options exercisable at June 30, 2012	667,114
Weighted Average Exercise Price per Share
Beginning Balance	$ 40.11
Granted	$ 52.03
Exercised	$ 39.54
Forfeited	$ 43.56
Ending Balance	$ 42.51
Options exercisable at June 30, 2012	$ 40.51
Weighted Average Remaining Contractual Term (years)
Options outstanding at June 30, 2012	6 years 6 months
Options exercisable at June 30, 2012	4 years 8 months 12 days
Aggregate Intrinsic Value
Options outstanding at June 30, 2012	$ 16,588
Options exercisable at June 30, 2012	$ 7,476