Earnings Per Common Share Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Earnings Per Share Disclosure [Line Items]
Net earnings	$ 26,421	$ 21,411
Weighted-average common shares outstanding, basic	42,114	49,929
Shares issued on exercise of dilutive options	4,894	6,693
Shares purchased with assumed proceeds of options and unearned restricted shares	2,965	4,293
Shares contingently issuable	2	4
Weighted-average common shares outstanding, diluted	44,045	52,333
Net earnings per common share, diluted	$ 0.60	$ 0.41
Anti-dilutive options excluded from calculation of weighted-average common shares outstanding, diluted	3,486	2,565