Other assets by major categories (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Line Items]
Net deferred tax assets (net of valuation allowance)	$ 424,193	$ 429,691	$ 250,568
Investments under the equity method	335,762	313,152	294,559
Bank Owned Life Insurance	238,870	238,077	239,103
Prepaid F D I C Insurance Assessment	34,634	58,082	129,093
Other prepaid expenses	69,524	77,335	66,719
Derivative Fair Value Of Derivative Asset	58,604	61,886	65,169
Securities sold but not yet delivered	71,007	69,535	37,752
Others	206,938	214,635	231,776
Total other assets	$ 1,439,532	$ 1,462,393	$ 1,314,739