Commitments, Credit Risk And Contingencies (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012 Commitments to Extend Credit [Member]	Dec. 31, 2011 Commitments to Extend Credit [Member]	Sep. 30, 2012 Standby Letters of Credit [Member]	Dec. 31, 2011 Standby Letters of Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Extended credit and standby letters of credit		$ 2,557,030	$ 1,943,889	$ 131,552	$ 113,268
Percentage of commitments to extend credit dependent upon the financial condition of the customer	78.70%
Settlement fund	$ 3,000