Business Combinations - Rollforward of Acquired Non-Covered Loans Without 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 without Deterioration of Credit Quality [Member]
Purchased Non Covered Loans [Line Items]
Balance, beginning of year	173,190	228,602	228,602	142,128	186,286
Additions due to acquisitions	0	0	0
Loan payments, transfers, etc.	(31,062)	(42,316)	(55,412)
Loans without Deterioration of Credit Quality [Member] | Non-Covered Loans [Member]
Purchased Non Covered Loans [Line Items]
Balance, beginning of year	381,588
Additions due to acquisitions	250,161		382,531
Loan payments, transfers, etc.	(50,026)		(943)
Balance, end of year	$ 581,723		$ 381,588