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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
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)	(15,496,941)	(13,550,710)	(15,396,215)	(14,783,078)
Weighted Average Number of Shares, Deferred Compensation Plans	(37,411)	(37,411)	(37,411)	(37,411)
Average unearned nonvested shares	(113,321)	(100,134)	(117,737)	(95,916)
Weighted average common shares and common stock equivalents used to calculate basic earnings per share (in shares)	98,267,229	100,226,647	98,363,539	98,998,497
Additional common stock equivalents (nonvested stock) used to calculate diluted earnings per share	243,258	226,754	214,837	161,660
Weighted Average Number Of Additional Shares Deferred Compensation Plan	37,411	37,411	37,411	37,411
Weighted average common shares and common stock equivalents used to calculate diluted earnings per share (in shares)	98,547,898	100,490,812	98,615,787	99,197,568
Basic Earnings per Share (in dollars per share)	$ 0.27	$ 0.25	$ 0.80	$ 0.81
Diluted Earnings per Share (in dollars per share)	$ 0.27	$ 0.25	$ 0.80	$ 0.81