Summary of Stock Option Plan Activity (Detail) (USD $)	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding, beginning of period, Shares	2,715,430	2,843,909
Granted, Shares	517,500	297,000
Exercised, Shares	(38,524)	(118,014)
Forfeited or cancelled, Shares	(51,250)	(18,250)
Expired, Shares	(158,850)	(256,250)
Outstanding, end of period, Shares	2,984,306	2,748,395
Outstanding, beginning of period, Weighted Average Exercise Price	$ 38.57	$ 39.22
Granted, Weighted Average Exercise Price	$ 36.81	$ 46.47
Exercised, Weighted Average Exercise Price	$ 30.49	$ 33.13
Forfeited or cancelled, Weighted Average Exercise Price	$ 40.18	$ 37.39
Expired, Weighted Average Exercise Price	$ 44.04	$ 57.00
Outstanding, end of period, Weighted Average Exercise Price	$ 38.07	$ 38.62