Assets Acquired In FDIC-Assisted Acquisitions - Rollforward of Acquired Loans Deterioration of Credit Quality (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2011
Balance, beginning of year	$ 16,698	$ 29,537	$ 29,537	$ 13,532	$ 30,167
Additions due to acquisitions		9,863	9,863
Balance, end of year	160,979	220,016	159,724			242,394
Loans With Deterioration Of Credit Quality [Member]
Balance, beginning of year	282,737	307,790	307,790
Change in estimate of cash flows, net of charge-offs or recoveries	(5,391)	(3,388)	(17,712)
Additions due to acquisitions		73,414	73,414
Other (loan payments, transfers, etc.)	(22,279)	(9,451)	(80,755)
Balance, end of year	255,067	368,365	282,737
Loans without Deterioration of Credit Quality [Member]
Balance, beginning of year	228,602	266,966	266,966
Change in estimate of cash flows, net of charge-offs or recoveries	(2,625)	222	1,376
Additions due to acquisitions		51,367	51,368
Other (loan payments, transfers, etc.)	(20,229)	(19,684)	(91,108)
Balance, end of year	$ 205,748	$ 298,871	$ 228,602