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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
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)	(15,821,469)	(15,496,941)	(15,761,114)	(15,396,215)
Weighted Average Number of Shares, Deferred Compensation Plans	(45,454)	(37,411)	(41,790)	(37,411)
Average unearned nonvested shares	(130,883)	(113,321)	(121,249)	(117,737)
Weighted average common shares and common stock equivalents used to calculate basic earnings per share (in shares)	97,917,096	98,267,229	97,990,749	98,363,539
Additional common stock equivalents (nonvested stock) used to calculate diluted earnings per share	197,545	243,258	188,255	214,837
Weighted Average Number Of Additional Shares Deferred Compensation Plan	45,502	37,411	45,502	37,411
Weighted average common shares and common stock equivalents used to calculate diluted earnings per share (in shares)	98,160,143	98,547,898	98,224,506	98,615,787
Basic Earnings per Share (in dollars per share)	$ 0.20	$ 0.27	$ 0.49	$ 0.80
Diluted Earnings per Share (in dollars per share)	$ 0.20	$ 0.27	$ 0.49	$ 0.80