Business Combinations - Rollforward of Acquired Non-Covered Loans With Deterioration of Credit Quality (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2012
Purchased Non Covered Loans [Line Items]
Balance, beginning of year	$ 25,493	$ 16,698	$ 16,698	$ 20,741	$ 30,849
Additions due to acquisitions	0	0	0
Balance, end of year	38,233	81,763	65,441			159,724
Non-Covered Loans [Member]
Purchased Non Covered Loans [Line Items]
Balance, beginning of year	26,189			29,064
Additions due to acquisitions	7,799		26,189
Loans with Deterioration of Credit Quality [Member]
Purchased Non Covered Loans [Line Items]
Balance, beginning of year	217,047	282,737	282,737	171,461	231,589
Charge-offs, net of recoveries	(8,099)	(30,371)	(35,306)
Additions due to acquisitions	0	0	0
Other (loan payments, transfers, etc.)	(37,487)	(20,777)	(30,384)
Loans with Deterioration of Credit Quality [Member] | Non-Covered Loans [Member]
Purchased Non Covered Loans [Line Items]
Balance, beginning of year	67,165
Charge-offs, net of recoveries	(4)
Additions due to acquisitions	29,280		67,165
Other (loan payments, transfers, etc.)	(4,440)
Balance, end of year	$ 92,001		$ 67,165