Earnings Per Common Share Data (Detail) (USD $) In Thousands, except Per Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Earnings Per Share Disclosure [Line Items]
Net earnings	$ 30,252	$ 11,105	$ 51,663	$ 333,633
Weighted-average common shares outstanding, basic	47,877	49,531	48,903	49,251
Shares issued on exercise of dilutive options	5,591	9,142	6,142	8,237
Shares purchased with assumed proceeds of options and unearned restricted shares	(3,305)	(6,183)	(3,799)	(5,469)
Shares contingently issuable	4	9	4	9
Weighted-average common shares outstanding, diluted	50,167	52,499	51,250	52,028
Net earnings per common share, diluted	$ 0.60	$ 0.21	$ 1.01	$ 6.41
Anti-dilutive options excluded from calculation of weighted- average common shares outstanding, diluted	3,285	1,472	2,915	2,729