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		12 Months Ended
	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2013 Loans with Deterioration of Credit Quality [Member]	Sep. 30, 2012 Loans with Deterioration of Credit Quality [Member]	Dec. 31, 2012 Loans with Deterioration of Credit Quality [Member]	Sep. 30, 2013 Loans without Deterioration of Credit Quality [Member]	Sep. 30, 2012 Loans without Deterioration of Credit Quality [Member]	Dec. 31, 2012 Loans without Deterioration of Credit Quality [Member]
Balance, beginning of year	$ 29,537	$ 29,537	$ 30,849	$ 16,698	$ 19,369		$ 282,737	$ 307,790	$ 307,790	$ 228,602	$ 266,966	$ 266,966
Change in estimate of cash flows, net of charge-offs or recoveries							30,371	(7,119)	(17,712)	11,554	3,861	1,376
Additions due to acquisitions	9,863	9,863						73,414	73,414		51,367	51,368
Other (loan payments, transfers, etc.)							(81,519)	(70,402)	(80,755)	(53,870)	(72,755)	(91,108)
Balance, end of year	$ 198,440	$ 159,724	$ 81,763			$ 242,394	$ 231,589	$ 303,683	$ 282,737	$ 186,286	$ 249,439	$ 228,602