Earnings per Share - Composition of Weighted-Average Common Shares (Denominator) Used in Basic and Diluted Earnings Per Share (Detail) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 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)	(17,695,829)	(15,788,359)	(17,707,057)	(15,730,604)
Weighted Average Number of Shares, Deferred Compensation Plans	(55,582)	(41,426)	(55,563)	(39,939)
Average unearned nonvested shares	(150,663)	(152,784)	(132,474)	(116,379)
Weighted average common shares and common stock equivalents used to calculate basic earnings per share (in shares)	96,012,828	97,932,333	96,019,808	98,027,980
Additional common stock equivalents (nonvested stock) used to calculate diluted earnings per share	213,982	173,095	180,052	185,023
Weighted Average Number Of Additional Shares Deferred Compensation Plan	55,615	41,426	55,615	41,426
Weighted average common shares and common stock equivalents used to calculate diluted earnings per share (in shares)	96,282,425	98,146,854	96,255,475	98,254,429
Basic Earnings per Share (in dollars per share)	$ 0.31	$ 0.24	$ 0.72	$ 0.29
Diluted Earnings per Share (in dollars per share)	$ 0.31	$ 0.24	$ 0.72	$ 0.29