Summary of Stock Option Plan Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding, beginning of period, Shares	2,715,430	2,843,909	3,131,142
Granted, Shares	529,500	297,000	412,250
Exercised, Shares	(90,624)	(120,064)	(326,823)
Forfeited or cancelled, Shares	(101,574)	(49,165)	(247,260)
Expired, Shares	(159,850)	(256,250)	(125,400)
Outstanding, end of period, Shares	2,892,882	2,715,430	2,843,909
Exercisable, end of year	1,630,382	1,686,930	2,037,159
Outstanding, beginning of period, Weighted Average Exercise Price	$ 38.57	$ 39.22	$ 39.16
Granted, Weighted Average Exercise Price	$ 36.84	$ 46.47	$ 42.72
Exercised, Weighted Average Exercise Price	$ 25.47	$ 32.82	$ 36.88
Forfeited or cancelled, Weighted Average Exercise Price	$ 41.45	$ 41.67	$ 44.49
Expired, Weighted Average Exercise Price	$ 44.05	$ 57.00	$ 44.91
Outstanding, end of period, Weighted Average Exercise Price	$ 38.28	$ 38.57	$ 39.22
Exercisable, end of year	$ 37.18	$ 37.69	$ 39.74