Long-Term Stock Incentive Plan (Detail) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding at the beginning of year	6,891,975	7,271,503
Granted	7,500	8,750
Exercised	(678,920)	(363,528)
Forfeited		(18,500)
Expired	(3,750)	(6,250)
Options outstanding at the end of period	6,216,805	6,891,975
Options exercisable at the end of the period	4,451,693	3,822,844
Options outstanding at the beginning of year	$ 15.33	$ 15.20
Granted	$ 18.67	$ 17.24
Exercised	$ 13.19	$ 12.65
Forfeited		$ 15.21
Expired	$ 12.15	$ 18.26
Options outstanding at the end of period	$ 15.57	$ 15.33
Options exercisable at the end of the period	$ 16.17	$ 16.16