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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
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)	(16,602,502)	(12,836,692)	(15,858,433)	(11,773,187)
Average unearned nonvested shares	(153,659)	(159,260)	(177,462)	(162,335)
Weighted average common shares and common stock equivalents used to calculate basic earnings per share (in shares)	88,807,294	92,567,503	89,527,560	93,627,933
Additional common stock equivalents (nonvested stock) used to calculate diluted earnings per share	6,452	11,198	3,938	4,850
Incremental Common Shares Attributable to Call Options and Warrants	0	0	0	0
Weighted average common shares and common stock equivalents used to calculate diluted earnings per share (in shares)	88,813,746	92,578,701	89,531,498	93,632,783