Earnings per Share - Composition of Weighted-Average Common Shares (Denominator) Used in Basic and Diluted Earnings Per Share (Detail) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Weighted Average Number of Shares Issued, Basic	113,914,902	113,914,902	113,914,902	113,914,902
Average treasury shares (in shares)	(18,103,611)	(15,821,469)	(17,840,694)	(15,761,114)
Weighted Average Number of Shares, Deferred Compensation Plans	(55,615)	(45,454)	(55,581)	(41,790)
Average unearned nonvested shares	(139,255)	(130,883)	(134,759)	(121,249)
Weighted average common shares and common stock equivalents used to calculate basic earnings per share (in shares)	95,616,421	97,917,096	95,883,868	97,990,749
Additional common stock equivalents (nonvested stock) used to calculate diluted earnings per share	220,268	197,545	191,119	188,255
Weighted Average Number Of Additional Shares Deferred Compensation Plan	55,615	45,502	55,615	45,502
Weighted average common shares and common stock equivalents used to calculate diluted earnings per share (in shares)	95,892,304	98,160,143	96,130,602	98,224,506
Basic Earnings per Share (in dollars per share)	$ 0.36	$ 0.20	$ 1.08	$ 0.49
Diluted Earnings per Share (in dollars per share)	$ 0.36	$ 0.20	$ 1.08	$ 0.49