Earnings Per Common Share Data (Detail) (USD $) In Thousands, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Earnings Per Share Disclosure [Line Items]
Net earnings	$ 27,494	$ 26,979	$ 79,157	$ 360,612
Weighted-average common shares outstanding, basic	45,689	49,138	47,831	49,216
Shares issued on exercise of dilutive options	4,981	8,368	5,756	8,303
Shares purchased with assumed proceeds of options and unearned restricted shares	(2,908)	(5,520)	(3,502)	(5,495)
Shares contingently issuable	4	9	4	9
Weighted-average common shares outstanding, diluted	47,766	51,995	50,089	52,033
Net earnings per common share, diluted	$ 0.58	$ 0.52	$ 1.58	$ 6.93
Anti-dilutive options excluded from calculation of weighted-average common shares outstanding, diluted	3,681	1,409	3,170	2,069