Earnings Per Common Share Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share Disclosure [Line Items]
Net earnings	$ 36,740	$ 27,494	$ 84,868	$ 79,157
Weighted-average common shares outstanding, basic	39,047	45,689	40,777	47,831
Shares issued on exercise of dilutive options	4,595	4,981	4,613	5,756
Shares purchased with assumed proceeds of options and unearned restricted shares	(2,810)	(2,908)	(2,859)	(3,502)
Shares contingently issuable	0	4	1	4
Weighted-average common shares outstanding, diluted	40,832	47,766	42,532	50,089
Net earnings per common share, diluted	$ 0.90	$ 0.58	$ 2.00	$ 1.58
Anti-dilutive options excluded from calculation of weighted-average common shares outstanding, diluted	3,184	3,681	3,397	3,170