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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Weighted Average Number of Shares Issued, Basic	105,563,455	105,563,455	105,563,455	105,563,455
Average treasury shares (in shares)	(16,609,505)	(16,602,502)	(16,617,616)	(15,858,433)
Average unearned nonvested shares	(99,502)	(153,659)	(103,696)	(177,462)
Weighted average common shares and common stock equivalents used to calculate basic earnings per share (in shares)	88,854,448	88,807,294	88,842,143	89,527,560
Additional common stock equivalents (nonvested stock) used to calculate diluted earnings per share	3,756	6,452	1,796	3,938
Weighted average common shares and common stock equivalents used to calculate diluted earnings per share (in shares)	88,858,204	88,813,746	88,843,939	89,531,498