Assets Acquired In FDIC-Assisted Acquisitions (Rollforward Of Acquired Loans Deterioration Of Credit Quality) (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended				9 Months Ended		12 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2012 Loans with Deterioration of Credit Quality	Sep. 30, 2011 Loans with Deterioration of Credit Quality	Dec. 31, 2011 Loans with Deterioration of Credit Quality	Sep. 30, 2012 Loans without Deterioration of Credit Quality	Dec. 31, 2011 Loans without Deterioration of Credit Quality	Sep. 30, 2011 Loans without Deterioration of Credit Quality
Balance, January 1	$ 29,537	$ 37,383	$ 37,383	$ 19,369	$ 41,106		$ 307,790	$ 252,535	$ 252,535	$ 266,966	$ 302,456	$ 302,456
Change in estimate of cash flows, net of charge-offs or recoveries							(7,119)	(18,815)	(25,787)	3,861	(11,604)	(16,886)
Additions due to acquisitions	9,863	24,094	24,094				73,414	124,136	124,136	51,367	35,439	35,439
Other (loan payments, transfers, etc.)							(70,402)	(36,899)	(43,094)	(72,755)	(59,325)	(46,538)
Ending balance	$ 198,440	$ 239,719	$ 242,394			$ 177,187	$ 303,683	$ 320,957	$ 307,790	$ 249,439	$ 266,966	$ 274,471