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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Weighted Average Number of Shares Issued, Basic	113,914,902	105,563,455	111,100,495	105,563,455
Average treasury shares (in shares)	(16,436,228)	(16,609,505)	(16,465,984)	(16,617,616)
Average unearned nonvested shares	(75,858)	(99,502)	(98,039)	(103,696)
Weighted average common shares and common stock equivalents used to calculate basic earnings per share (in shares)	97,402,816	88,854,448	94,536,472	88,842,143
Additional common stock equivalents (nonvested stock) used to calculate diluted earnings per share	54,654	3,756	42,018	1,796
Weighted average common shares and common stock equivalents used to calculate diluted earnings per share (in shares)	97,457,470	88,858,204	94,578,490	88,843,939