Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Y
Schedule Of Stock Options [Line Items]
Shares Subject to Options, Outstanding, beginning of the year	1,132,546
Shares Subject to Options, Granted	431,667
Shares Subject to Options, Exercised	(204,082)
Shares Subject to Options, Forfeited or expired	(275,938)
Shares Subject to Options, Outstanding, end of the year	1,084,193
Shares Subject to Options, Exercisable, end of the year	558,768
Weighted Average Exercise Price, Outstanding, beginning of the year	$ 57.17
Weighted Average Exercise Price, Granted	$ 59.85
Weighted Average Exercise Price, Exercised	$ 51.66
Weighted Average Exercise Price, Forfeited or expired	$ 60.50
Weighted Average Exercise Price, Outstanding, end of the year	$ 58.43
Weighted Average Exercise Price, Exercisable, end of the year	$ 57.53
Weighted Average Remaining Contractual Life In Years, Outstanding, end of the year	7
Weighted Average Remaining Contractual Life In Years, Exercisable, end of the year	5 years 4 months 24 days
Aggregate Intrinsic Value, Outstanding, end of the year	$ 14,037
Aggregate Intrinsic Value, Exercisable, end of the year	$ 7,772