Shareholders' Equity - Additional Information (Detail) (USD $)			12 Months Ended			1 Months Ended		1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Nonvoting Common Stock	Dec. 31, 2011 Nonvoting Common Stock	Dec. 07, 2010 Nonvoting Common Stock	Mar. 31, 2010 Nonvoting Common Stock And Class A Common Stock	Dec. 07, 2010 Nonvoting Common Stock And Class A Common Stock	Dec. 31, 2012 Nonvoting Common Stock And Class A Common Stock Maximum
Class of Stock [Line Items]
Treasury Shares	15,031,741	15,111,635
Additional authorized shares purchased	4,044,655
Nonvoting common stock repurchased			1,236,689	5,075,675
Preferred stock, authorized	1,000,000
Common Stock, Par Value	$ 0.50	$ 0.50			$ 0.50
Common Stock, Shares Authorized	225,000,000	225,000,000					225,000,000
Maximum percentage of cash dividend on Nonvoting Common Stock higher than any dividend paid on Class A Common Stock								50.00%
Stock split conversion ratio						1.5
Percentage of stock dividend on both Nonvoting Common Stock and Class A Common Stock effected by stock split						50.00%