Issued and Outstanding Stock Options (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Long-Term Stock Incentive Plans:
Options outstanding at the beginning of year	6,216,805	6,891,975
Granted	7,500	7,500
Exercised	(603,169)	(678,920)
Forfeited	(2,450)
Expired		(3,750)
Options outstanding at the end of period	5,618,686	6,216,805
Options exercisable at the end of the period	4,988,124	4,451,693
Options outstanding at the beginning of year, weighted average exercise price	$ 15.57	$ 15.33
Granted	$ 17.11	$ 18.67
Exercised	$ 13.98	$ 13.19
Forfeited	$ 16.15
Expired		$ 12.15
Options outstanding at the end of year, weighted average exercise price	$ 15.74	$ 15.57
Options exercisable at the end of the year, exercise price	$ 16.06	$ 16.17