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, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 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)	(16,445,760)	(11,584,636)	(15,480,232)	(11,232,622)
Average unearned nonvested shares	(195,303)	(184,230)	(189,561)	(163,897)
Weighted average common shares and common stock equivalents used to calculate basic earnings per share (in shares)	88,922,392	93,794,589	89,893,662	94,166,936
Additional common stock equivalents (nonvested stock) used to calculate diluted earnings per share	16,611	16,954	9,888	10,895
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)	88,939,003	93,811,543	89,903,550	94,177,831